It would probably be better to do this in spring as they start to emerge. They don't like too much disturbance and can sulk for a while. So it's best to chop through the edge of the clump and just lift away the parts that you want to move rather than lifting the whole clump. They have thick fleshy roots, so dig down carefully or they break off. It is a good idea to pot up small divisions and grow them on for a year to get their roots grown well, then plant out next year.

Propagation according to my RHS manual is to dig up and divide in early Spring and replant the sections immediately. Or discard pieces you don't want.

i do mine in spring too. it allows me to see what is where and where I want it.