If its a fully hardy one then yes you can trim/cut it back and it should resprout from the remaining stems. The bits you cut off could be used as cuttings. Pop about 2-3" of the tip into good compost and keep in a warm place with plenty of light. Then you will have some new plants too.

Mine are in pots and have overwintered in the gh(too exposed here)and have flowered all winter, I cut them back by half bringing the flowers indoors then gave them a feed, all shooting well, better get them out soon I think they're starting to flower again!

Mine's been outside all winter and is flowering well already. I've never had one before so thanks for the tip about cutting them back.