Do you want to do it correctly? Sure, you can just hack it down and it will probably recover and just regrow with thicker foliage above the cuts. These are trees, and if they don't want trees, they should remove them and plant something else. Others have mentioned it, but there are many other types of crapes that would fit the need better. Or just a different plant. When crapes are hacked like that, it opens them up to disease and pest infestation. I did this at a clients house because they insisted that the trees were too messy around their pool area but they hated to cut down such a beautiful type of tree. The next summer, they looked terrible and eventually got black sooty mold so they had to pay to have them treated. Now, they still don't look good and they are talking about removing them completely. It's all about knowing how to prune. If a customer demands it, then go with it. But if they ask your opinion, be honest and try to avoid hacking a tree into a bush. Crape myrtles never look the same afterward. Best cut is to clean up the bottom 1/2 - 2/3 of the tree depending on its size to create a tree look with a full canopy.
Walker, Toro, Stihl