as far as I know Rozanne hates being divided. Others have told me this. Mine are in place four years and havent been touched. You could try one plant first. I personally would do the division after the plant has died back provided there is still warmth in the soil which will encourage new root growth

I have been asking around how todivide my Rozanne. I will try this weekend to cut a branch below a node and try to propagate the branch. We will see. I will post the result of my success or failure later.

I would wait until Spring time. I divided my two Rozannes this past Spring so that I now have 4 plants. I interspersed them with Lamium (dead-nettle w/golden leaves, pink flowers) and they look great together.