Can i make the Nitro Rustler 2.5 a 2 speed transmission? Or can i make it a 4 wheel drive?

Probably not.

there is one guy who made a 4wd nitro rustler. you might be able to find him on the traxxas boards, but it would take way to much money and effort to do that. no one has been successful in making a 2 speed. there have been guys who tried by converting them 4-tec belt drives and all that, but the nitro rustler is fast enough and doesnt need a two speed. and if you want 4wd it would be easier to get an MT or an hpi nitro mt-2