No, won't hurt them unless you think your first frost is so soon that the new growth that will be stimulated won't have time to ripen/harden off before it.

There are a number of my own type 3's that I cut back about 1/2 of their size, water and fertilize, and they will give me a 2nd flush in the late summer/fall here in Evanston: Polish Spirit, Emilia Plater, Hagley Hybrid, Prince Charles and Viola are my best candidates.

Feel free to email me/pm me directly if you have questions. HH is done first and thus is pruned first, and it's about to start its second flush in about 2 weeks.

Great info. Since you're 1.5 hrs south of me, it should work for me as well. Which 1's have you noticed that it does not work on?