That's basically what we are trying to figure out with the Crape Myrtle that is in the front yard. How to prune it without hurting it. My husband did cut out a couple of dead branches from it right after we closed on the house, but was didn't want to do any more for fear of hurting it due to it being early April. At least it's definitely alive, just not blooming. I also wouldn't know where to start on a rosebush. Good luck.