Hello and welcome!
I think this is a great question, because it’s representative of those many of us have as we are dipping our toes in, or starting to dig deeper into customizing our input devices. “Can I make this board sound more like that board?” is such a simple question on its face, but a true answer is less so - still gonna do my best to give you a useful one, though. I’m known around here for novel-like posts of my own; indulge your verbosity! 
TL;DR answer just in case: “Probably not, but I encourage you to try some stuff anyway because you might have fun, learn some stuff, and get a different result you like.”
I’ve never used either board you mentioned, but I looked them both up - and while I’m not 100% certain where the difference is coming from, I have some ideas.
Why are they as they are?
Both appear to use a soft plate and layers of foam to improve acoustics, but it looks like the method of holding the internals to the chassis might be different, and this can have a pretty profound effect on how a board sounds (and feels).
The 75% looks to have what I’d call a “traditional” “gasket mount” - that is, all the operating bits are insulated from and held to the chassis by some kind of soft material, usually a piece of foam on either side of a tab extending from the plate. When paired with a soft plate, this usually has the effect of absorbing higher-frequency vibrations and removing harshness from the character of the board. The “traditional” qualifier comes from the fact that there are lots of variations on this method, and the one used by this board looks to be one of the more tried-and-true / simple “foam pad sandwich” types as opposed to a series of specially-shaped little silicone parts that fits in a set of slots, for example.
It’s a little less clear exactly how that 100% is put together, but Skyloong’s website lists the construction method as “top gasket mount”. This is a great example of what I’m going to call “muddy waters”, and few waters in the world of keyboards are as muddy as gasket-mount swamp. I mentioned above that there are many approaches to “gasket mounting” but that they all have in-common an isolation of the chassis and operating parts with something soft. This is true right up until folks start adding other qualifiers to the term - this is a sign there’s some reason they don’t feel comfortable just calling it “gasket mount” despite the wide diversity of approaches contained in the term. Woo, marketing!
“Top mount” is another well-established style, and it usually just refers to screwing the internals directly into the top half of the chassis - generally around the edge, and by the plate. Lots of people prefer this style for lots of reasons, but it does tend to sound and feel quite different to gasket mounting. Instead of having a shock-absorbing layer completely separating the chassis and the rest, they are joined with a hard connection with the plate potentially acting as something of a drum-head depending on its material.
So - and I’m making a leap of assumption here so bear with me - I think “top gasket” probably means that the plate is attached directly to the top but with some kind of insulating material dampening vibrations (or “breaking the transfer of forces”) between the chassis and inner assembly. (I think most folks over the years have just lumped this in with top-mount, only making the distinction of the dampening pads in the list of features rather than calling it a different mounting style.)
Top-mount-with-pads is not going to be the same as regular top-mount, but I believe in most cases that’s going to be much more similar to regular top-mount than any possible iteration of “true” gasket mounting where the “gasket” (soft thing) is itself the mechanism holding the inner and outer parts together. Here (I think), we have some kind of hard fastening device (whether metal screw or plastic clip) holding the inner parts to the top chassis, just with some insulation in-between to mitigate the most harsh of vibration transfer.
Mounting style is far from the only factor that affects sound and feel, but its one of the core ones, and the one I suspect to be the biggest player in these two boards sounding so different.
Can I make them more like each other?
The honest short answer is “no” - with the longer answer starting “maybe a little, maybe more, probably not - but maybe worth a shot.” I say worth a shot because a.) there’s a slim chance you might get the result you’re hoping for and b.) even if you don’t, you’re very likely to learn something in the pursuit. Here’s some stuff to explore / try:
Fiddling with the mounting:
Again I’m not exactly sure how the Skyloong is put together, but if it uses screws to hold the plate to the top and those screws are long enough to accommodate them, it may be possible to further dampen the hard connection with silicone o-rings or foam pads between the screwheads and the plate. (Doing it with o-rings has the fun name of “burger mounting” 
) It really depends on the board whether or not this is viable, and while its doable in some commercial boards, I’m going to guess there won’t be room to fit in anything else in-line with the screws here. Still might be worth a look, just in case.
Another potential mod for this board, depending on what their “gaskets” actually look like, is fashioning some of your own from a different material. They don’t show them on the site, but do call them “silicone-soft”. This is a great time to mention that “gaskets” come in lots of different materials, and that silicone is actually one of the most firm among them. If they’re a nice simple shape, say a rectangle with a hole to accommodate a screw, it might be easy enough to shape some of your own from a more vibration-deadening material like poron or car-audio foam.
The tape mod:
This one is subjective (I guess they all are), but might be one of the easiest to do (and un-do) mods around - so as long as the Skyloong isn’t a huge pain to open, I say this one is totally worth a shot. The “tape mod” is simply applying a thin sheet of some material to the back of the PCB; most people literally use masking tape, but some kits come with / some vendors sell adhesive plastic sheets specially shaped for a given PCB. (I also think there’s a good chance your 75 has this from the factory, but I’m not certain.)
I use wide signage tape because that’s what I have around. I can’t tell you exactly what this will do to the sound of a given board, but I can tell you that it’s a very popular mod with lots of positive feedback in the realm of sound - and it’s really easy. There are quite a few before/after comparison videos on youtube of various boards getting the tape mod if you’d like to get an idea of what effect it will have.
How do I even get it open?
Since I’m not sure how this model is put together I can’t tell you exactly, but I can help prepare you for probing.
Most boards are put together with screws, clips, or a combination of both. Just from the look of the exploded diagram on the site, it looks like the Skyloong might be put together with clips. These aren’t as easy to deal with as screws, but the right tools go a long way, and thankfully they are readily available and inexpensive. Any given “console controller disassembly kit” on the internet will probably have everything you need to take apart most keyboards - and if you’re sure it’s just clips, you can just get a “spudger” or two - basically little levers with a flat end to help you release the clips without breaking them.
Looking at the bottom of the board, if you see screw holes, go for those first. If you’ve got all the screws out and it’s not coming apart easily, look for any stickers (or sometimes adhesive rubber feet) on the bottom that might conceal another. If you’re sure you’ve gotten all the screws (or there aren’t any) and the board isn’t coming apart easily or at all, you’re likely dealing with clips.
In almost all cases, clips will be around the edges and can be released with a flat tool from the underside. I don’t recommend a screwdriver as they tend to be a bit too thick, but an old credit card can do in a pinch if you don’t want to go spudger shopping. General rule; take it slow and easy, don’t force anything, and it should come apart pretty easily once you’ve found all the fasteners.
Is it worth it?
I can’t answer this for anyone but myself, but for me it’s pretty much always been worth it to poke around inside a board. In the 7 or so years I’ve been doing it I have had a couple worst-case scenarios of just totally destroying one - but those all involved a hot soldering iron and a lack of patience - and even then they were genuinely educational experiences. I learned not only how to improve my soldering technique (which you don’t even have to mess with these days unless you want to), but I also learned a lot about the individual model boards I was fiddling with. For me, a curious tinkerer, that was super worth it. For someone who just wants the dang board to sound great, maybe not.
While I honestly don’t think there’s anything one could do to give your top-gasket fullsize the same sound character as your gasket-mount 75%, I do think there are things you can do to make the sound more enjoyable to you. Aside from what’s listed above, I do recommend exploring switch options to find something that might compliment the existing chassis in a way that’s pleasing to your ear. I wouldn’t expect it to be pleasing in the same way as the 75, but I’m confident you could gain some ground there. The great thing about hot-swap boards is that you can try an individual sample switch in your board and swap it back out again easily.
Switches!
While I think mounting style and plate material are probably the biggest players in sound character for a chassis, switches themselves also play an enormous role in the sound. Of course as you’ve already experienced, they’re only part of the picture and on their own aren’t going to necessarily carry the same experience from one chassis to another. That said, they can still drastically change the character of a build all on their own.
This in mind, I’d recommend trying a switch sampler of some kind. Plenty of vendors offer sample packs of varying sizes, but depending on how comfortable you are with internet strangers (or maybe if you have a PO box), I’d be more than happy to send you one from my fairly absurd collection - a portion of which I keep purely for sharing in situations like these. I genuinely enjoy curating sample sets for folks, and I could send you a pretty wide cross-section of what’s available. If you’re interested in a switch sampler you can shoot me a DM here on KeebTalk or send me an email: david@switchbox.studio
Aside from that please feel free to ask any questions you might have right here in the thread. I may not have an answer, but I’ll at least take a whack at finding you one.
Again welcome to KeebTalk, and thanks for asking such a great question. Cheers!