RE: CG Change?
Rudder won't affect the CG for pitch but you may notice that in turns you need to use a bit of top aileron to keep it from winding in. By adding that much "fin" area you've changed the spiral stability value and an overly large fin area tends to make a design want to tighten the turn. Like most things in life fins have a happy medium. How your model flies will be determined by where on the scale the original design was.