Re: HSH rg prestige, will a HH pickguard fit?
It depends on the models. Not all RG pickguards are interchangeable. There's usually misaligned screw holes, etc. Then there's the neck pocket--some are curved and others straight.
Your best bet is to get a custom made guard. Try Pickguards Paradise, Pickguards Heaven or Greasy Groove. They usually require that you send in a tracing of your guard, but you'll get one that lines up perfectly.
I can personally vouch for Pickguard Heaven and Greasy Groove. Greasy Groove made my RG550 Space Invaders guard--look around the forum and you'll see it.