Yes, you can reveg them. Just leave a few lower branches intact, when you harvest. It will take from 4 to 6 weeks of lights on 18/6, to get them back to veg growing. Ignore the weird leaves, that will come out at first. In a couple of weeks, they'll all start looking alot better. I also find, repotting up to a bigger pot helps. When you do this, adding some fresh soil with a little earthworm castings mixed in, helps restore them. Otherwise, they're probably already rootbound, and that slows them down a bit. Hope this helps.