I would top during veg like I would believe everyone else would do according to books, videos, comments from other old time growers, etc..... If you got a flower going on, why would you want to hack it off ? Some people would be worried about stress, but could you really stress it out when a plant is already flowering? I'm not sure, but I do know someone that tried to re-veg 2 favorites a few years ago. He had left a few very small branches on the bottom of the plants and switched lights back to 24 and fed with a higher nitrogen fertilizer ratio. They started coming around growing new leaves and small limb . Would you call this re-vegging ? I guess it all depends on why you would want to top in flowering to begin with.... But I got to hand it to you Bro... your thinking of some neat shit. If you do decide to try it, please keep me posted because I would be very interested in the end results and smoke quality.