It would seem to me, that if you add weight to the rear, dynamic spine would weaken. The arrow would be heavier, adding more resistance on the shot. I would think that this would cause the arrow to bend less. Think of adding a pound weight to the rear. The arrow would travel very slowly and the needed spine to keep the arrow from bending, would be very light.

I completely agree with Arthur about the effects on FOC, which is why I never add weight to the rear. I don't dip my arrrows, use wraps, vanes, or any other heavier items on the rear. Randomly changing dynamic spine and lowering FOC is a double wammy in my opinion. The ideal arrow backend is light and has lots of drag, and adds good spin to the arrow.