You're not altering the genetics at all; the plant just expresses the genetics differently than it ordinarily would if it's under a great deal of stress - and yanking a flowering plant that was ready to die right out of a 12/12 light cycle and slamming it into 20/4 and forcing it to go back to veg is extremely stressful to the plant.
What you're seeing with the single-leaf structures and weird, whorled leaves is not a genetic aberration, but hormones. The plant is confused, and doesn't know whether it's supposed to be flowering or vegging. It's still producing a full load of flowering hormones, and now suddenly the light is all wrong for flowering and it automatically starts producing vegetation hormones in response to the light cycle. So yeah, it definitely looks like a mutant, because it's basically trying to be two different plants at the same time, and doesn't know what to do.
You just have to give it plenty of time. If you let it go solidly back to veg stage before putting it back into flower, it should be fine, and give you the same nice, dense buds as it did on the first harvest. I think most of the problems people have with revegged plants stems from not giving them enough time to go fully back to veg before putting them under 12/12 again. I always wait until I'm seeing 5-leaf sets, although some may feel that's being unnecessarily anal. I just believe in taking a little extra time to do things right the first time.
I have some clones flowering now that I cut from plants in the first week of bloom over 3 months ago, and it was just 2 or maybe 3 weeks ago that they were finally revegged enough (IMO) to put back into bloom. And even then, boy - did they snap back into flower fast! I only had them under 12/12 for 3 or 4 days before they were already in flower. I barely had time to cut clones before they were already sprouting white pistils all over the place. Even though they were fully vegged, part of them still apparently thought they were supposed to be in flower, and couldn't wait to get back to it.