There is a lot of different grades in metal polishes. Chrome, plastic chrome, aluminium, steel, and so on. Usually it is good to start with a "softer" one, and if needed, then change to a more coarse one. If you are afraid of wearing out paint, then start with a "paint scratch remover" or "plastic scratch remover". All these should be found in car equipment stores, try Halfords in UK. Brands like Autosol, Sonax and Farecla are old trusted brands.
Hmmm. When you say 'partially dismount' do you mean I should partially dismantle the lens, ie take it apart to a some degree?
If so then all I can say is : "Eeeeeeeeeek! Nope, no, no, nope. I'm far too 'yellow-bellied', 'lilly-livered', too much of a 'cowardy-custard' to even think of doing that."