From what I've read, you can cut back the new growth after it flowers, but it doesn't do well with pruning the hardwood branches. The article also said they were short lived, but I've had one for about 10 years.

The always-valuable San Marcos site says of rockrose (Cistus and Halimium):

"As a group they resent hard pruning and while they can be trimmed back
lightly and even gently formally shaped in late fall or winter, this
action is often at the expense of flowering."

I've read the same as hoovb states, but might depend on the variety.

I had a cistus Bennett's white rock rose from local nursery distributed/grown by Monrovia and trimmed it just couple inches and that led to it's death. I was hoping to thicken it. I finally found 6 more and not touching them.

I have several cistus corbariensis and trimmed the 3 oldest last year quite a bit and they grew back like weeds. So many buds their branches hung down to the ground.

I had one cistus purpureus never touched it and it died after 5-6 years. My city has them growing everywhere in landscaping and I'm willing to bet they get trimmed.