Dual crown fork or not? I currently own a 2015 GT Verb Expert. And after watching a Red Bull rampage video I started wondering can I put a 200mm fork on my Verb Expert. Or does my head tube need to be more angled. And is it possible that it could snap my frame if I install one?
Putting a longer travel fork on a bike not designed for it will alter the geometry of the bike, and usually the handling.  Depending on the amount of change, it might be barely noticeable, or it could also appreciably degrade the ability of the bike to be ridden.  You could put a 200mm travel fork on a road frame, but the resulting geometry would render the bike unfit for anything serious.

The change you are talking about will likely result in a rideable but slightly awkward ride.  It's unlikely you'll snap your frame (highly unlikely).  However, it's far more likely that if you use the front fork (a 200mm dual crown monster) to it's full potential, you blow out/prematurely wear the rear shock which is not designed for that kind of abuse.  Considering what a fork like that (or a replacement rear shock) costs, you'd probably be better off selling that bike as is and trying to by a bike more suited to the type of riding you are planning.