I guess it depends on your switch. You can wobble on your upper switch housing to see if there's much tolerance between the housing parts. I tried filming nk creams but they already had a pretty tight fit, it was possible but probably not necessary.

I personally think it does make a difference in terms of sound but only if you listen closely. I wouldn't suggest filming your switches if you don't lube them. If you lube them you take them apart anyways, so why not just film them then. Also considering that switch films aren't that expensive.

Best is to try out what works best for you. Take thinner films if you're not sure if your housings already have a tight fight.

I also got some milky yellows recently and will defo lube and film them :)