I only let the growth tip grow up to the point where I can easily get in with my scissors and make the chop. It may look like this slows down the plant temporarily, but if you look the next day at the accelerated growth of all the lower nodes as a result, it can be seen that topping does not actually stun the plant.
I would not recommend doing anything to the plant after flipping the lights. Some people defoliate even up to the end of stretch and I do not agree with that practices or what you are proposing. Flipping causes fundamental changes in the plant and so does topping. It makes no sense to me to do both at the same time so as to confuse and possibly stun the plant. Top, and wait 3 days or so before doing anything else. Defoliate a week before the flip so the plant can recover first. Topping is so as to cause accelerated growth in the lower nodes, it isnt just to make the plant shorter. Do that, and then wait a week to see what happens... don't just rush into the next process.
I actually think that topping during stretch would double the stretch motivation in the lower nodes and I think stretch would get worse, not better, since you would now have two biological processes in action telling the plant to stretch.