I replied in your first post.

I have always 'pruned' my clematis when it has been growing, it tends to come out into the garden if I don't and I prefer it growing up the fence. It doesn't seem to have done it any harm and it comes up year after year as strong as ever.

Pruning clematis does depend on what time of it flowers too. Cutting yours back shouldn't kill it unless its a really drastic prune, but ou may lose next years flowers.