Can you add a BOV(blow off valve) to a toyota supra that has factory twin turbos.?

and also i plan on putting a new twin turbo engine, and i was wondering, will the transmission still stay at a 5 speed manual, or would i have to change it so that it could be a 6 speed. Also with the computer, that makes the engine know how to use the manual, how do I get that, or does the mechanic do that?