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I wouldn't recommend it. I've read that causing too much stress can cause plants to go male/hermy when it is too close to flowering.
I doubt you would see much vertical growth or benefit from it anyway. I've found that it helps to consider, it is the same plant (whether topped or not) that produces the end result. It might have to work all that more hard too support the extra growth and effect quality.
I would just leave them be at this stage. I topped half my room by the 5th node, and it works well as long as you stake them up. They're getting pretty heavy.