If I were to guess I would say the friction needed to do this would be fast or take quite a while to have a meaningful effect. Thinking of just doing it by typing I think of the physics like Uma Thurman in Kill Bill trying to escape the coffin scene. There just is so little force, over such a small surface area for a short period of time. That’s why I am thinking a break in machine might get you the result desired.
As far as easily cleaning off that is going to be difficult because it needs to be oil versus water based to last in the which during the break in period. I think a few washes in the ultra sonic cleaner at a minimum would be required.
Plastic is different then wood but I am hoping it won’t require progressively less gritty paste to achieve the smoothness desired.
I am hesitant to admit this but, based on this post, just for fun I tried this with toothpaste on a couple of switches. Toothpaste can be used to polish out car scratches so it wasn’t too far out there of an idea. The grittiness could be felt when actuating the switches but at the end of the day it did not have a meaningful impact. At least not after just 3 minutes to actuating the switch. Probably due to the hardness of the switch vs the aggregate in the toothpaste (which should not be a problem for the diamond paste). Also it was a nightmare clean out by hand. Just to be clear, I do NOT recommend toothpaste in switches!
I agree the materials and manufacturing going into switches are getting more and more advanced. The likely hood of finding something that will work is low but when you find something that makes an advancement even if it is a little one it is pretty amazing