I've been doing that since linux "mepis 3" came out and for FREE 
So have I even triple boot but mac books are the Shit.
You can buy those latex "keyboard condoms for macs but nothing else (saved my mac from several spoilage over the years, can get hard she'll cases for them.
You don't have to use apple specific replacement parts I've got 8 gig of ram I installed my self and a 1tb solid state hard drive and it's still a good machine running the latest version of osx
