yes you can but not too hard as it may not recover. you could take seeds from it and grow them on just incase your pruning is too severe.
welcome to GoY too.

Hi, Sue. Do take some seeds, because in a hard winter, you could lose them. They are too beautiful to lose, aren't they? They do get big though, so when mine set seeds, I just cut the stem back quite hard, rather than just cut the seeds off. Hope this helps. Annie (Cumbria)