Can I prune a 20ft Ceoanothus tree ?

I have seen pictures of these when they have been cloud pruned they look great.

I had one years ago and I used to cut it to keep it in shape after flowering.
My book says cut back hard in Apr.

It is normal to trim back after flowering to keep it in shape. They are tempremental plants and who knows what a heavy cut-back might do but it sounds like you have no choice , so good luck.

They say not to cut into old wood, If the one branch has broken off with the snow I would just shape the rest after flowering, if that is successful do the whole thing gradually. If I were you I would hate to lose it.