Only prune a Limelight late fall thru early spring before new growth begins. They bloom on new growth. You can shape them however you like, but the blooms will be smaller if you do not hard prune. I did about 2-3 feet this year and am thinking of trying 12 inches or less this year. But I wait till early spring so I can enjoy the dried blooms through winter.

I cut mine down to 2 feet this year and the blooms are quite large in the end, but they also get too heavy even for the already rather strong stems. I think that I may try the suggestion that George had and try to just selectively prune it so that there will be a mixture of longer and shorter stems to try to have the best of both worlds.