I know that most spring bloomers are pruned back right after flowering so the blooms for the next season aren't affected. I just finished pruning one of my weigelias but it was mostly new growth and side shoots at the base that had gone too wild just to give it a little more shape and definition.

Penny

I wouldn't be afraid. It's not very frosty yet and they do often start to even grow back. I just did my spirea and they look like they are already growing after a week. I think it takes the weight off and provided the weather isn't awfully cold, they do get a burst of energy.
I have cut spirea after bloom and, even before if it was too large and I had to sacrifice blooms. And...they bloomed anyway. : )

I forgot to mention...don't hack it too low to the ground. I took 12 - 18 inches. If you cut it way down too low, it may not recover.