I am looking to buy carbon fiber mirror covers from JPcarbon, there listing doesn't offer any details so is this just a cover for the mirror a whole new mirror and will installing this part be a hassle?

 

All the mirror covers are just the back covers, at least all the ones I've seen.
I wrapped my covers a while back (and have since gone to hydro-graphic print) so here's a thread that will show you what's involved
https://www.myg37.com/forums/d-i-y-i...or-covers.html