If your Limelight has been planted in a place where it can attain its estimated size at maturity, you should not need to prune it until exceeds its boundaries... typically after 10 years or so. The plant label for Limelight suggests a size (tall & width) of 8' or more. If you are having to prune it often to keep its size in check, you may either need to transplant it elsewhere (when dormant) or use a more compact shrub in that spot. For example, Little Lime is almost like Limelight, just not as tall/wide. The only difference I have noticed is that the white bloom color of Little Lime is not as pure white as that of the regular Limelight blooms.
Pruning of paniculatas should not be done now as this is the time when they typically bloom. Besides, as you pointed out, temperatures are now just terrible; since pruning sometimes forces the plant to go into grow mode, do not prune when temps are in these ungodly hot ranges. I prefer to prune when they have gone dormant. Some people therefore prune in the Fall or in Winter (before leaf out).
Since you have already pruned, keep the shrub well mulched and keep the soil as evenly moist as you can. Water when the top 4" start to feel almost dry or dry. Do not fertilize in the middle of a heat wave or when a plant is stressed due to pruning or other issues.
My Little Lime is handling the daily 100s here in Tx very well so far. I have not pruned it since I got it several years ago. Yours should recover by next year. It is a very vigorous shrub.
