[rick3000]

Nothing wrong with making some changes, and it is not hard to keep everything fully reversible. The radio is a 5 minute swap if you keep the original head unit, and I can't see something invisible like a speaker swap affecting the value. Unless you are bolting a giant spoiler to the back you should be fine. It is your car, so make the changes that you enjoy! I personally try to keep all of my modifications in the spirit and style of the 986.

The only place I would watch out is if you start permanently modifying parts that are exclusive to the Special Edition, because you could run into issues if you ever wanted to replace them back to stock. I'm specifically thinking about the Cocoa interior, were used parts are extremely rare.