If youre careful you can do anything. I just helped a friend move his vegging plants from 7 gallons of Promix into his new Ebb n Gro system. I know its a little off topic and not the same situation but let me explain. His plants were vegging for 2 months in 7 gallons of Promix so they were rather big to be doing any transplanting without the risk of shocking them. He had clones set back in case the swap didnt workout so we werent too worried of losing plants. It took a lot of time and careful rinsing but we were able to get it done. I guess it all depends on your time schedule and if you know how to care for a plant that may have been shocked in the process.