Well in a way to answer 2 questions there at once. It is possible to put your plant back in veg after its harvested just leave some follage at the bottom of the plant. Throw it back on a 18/6 cycle or 24/0 and you should be fine. Or you make hash out of the trim/leaves/stalks. With that being said, if your plant can go back in veg you can clone but why during flowering? If you do that your taking away their "solar panels" for energy and transfering sugars and all that good stuff. You can lollipop your plants right before flowering (trimming the bottom 1/3 of the plant) snag some clones off that.