Are you saying it was done by someone else? How much did they charge you? Warranty isn't a consideration but obtaining the part may be difficult.
Yes it was done by samsung's affiliated repair shop in France, it was because le little plastic was scratched very hard with sand (beach etc) so all photos i would take were blured with a white fog
I'm not a huge fan of opening anything except my computer but i'm sure it could be done easily since it's just opening and cleaning (or whatever, i have not really understood what happened to you camera
to find the part, i found someone on xda that had provided a link to the original parts of the samsung galaxy S2 for like 10 bucks which was very difficult to find because as a french i wasn't knowing the exact word for the "backplate or whatever it is"
now i know it, just google "galaxy S2 original housing" and you'll find plenty results like this one here
(assuming you have to change the whole back cover
and last things it cost me 25€ for the back only with no extra battery cover which is a bit overpriced :V