I believe you wanted to cut your vegging plants in half. I hope I said you could do that and take cuttings for new clones. Then you could root the new cuttings and start all over with new clones. Or you could keep a big plant as a mother plant to clone from whenever you want.
You don't ever need to mess with the roots if you are in dirt. I don't remember what your medium is.
Did any of this make sense? If not, i blame no coffee or smoke yet this morning. lol Let me know how I can help better.
No you don't want to cut the roots off of the clone and try to re-root it. Once the plant is growing bigger in the veg stage, it would be too hard to get the whole plant to pause and go back to rooting again. If you need more time on your clones that are already growing too big, then you can prune them way back like people do shrubs and then it will grow back and take that many weeks to get back to where it was when you pruned it back. It will also come back more bushy.