It is possible to mount a tremolo bar on your guitar, but as its an SG (same applies to LP's) its built for tone, so it would be wiser to get a Les Trem or Stetsbar (both of which don't require mounting, so if you ever change your mind, you can just pop 'em off). Of course, you're not gonna be able to dive bomb like crazy on it... As for the third pickup, you may as well find a luthier to do it, because once you have routed the third pickup, chances are that the three-way toggle switch will have to be swapped out for a 5-way one.