I don't think makes any difference at all.
Vr is a function of your stall speed but limited by a few other speeds if your in a twin. 1.3 Vs springs to mind unless limted by Vmca
CofG is a balance issue that you have to be within.
I have a spread of Vr of 15knts through the weight range on my turboprop.
CofG is used to set the trim for departure and thats it for takeoff planning. At the forward limit and at the rear limit Vr remains the same.