yes you can do it. be careful with the root ball, but try to get as much of the mg out of the root mass as you can. if it's too dense, just transplant it normally. i wouldn't feed it for a couple weeks either. FF soils have about 2 weeks worth of nutrients. either OF or HF are good, but OF has more nutes in it imo. a lot of people throw in some light warrior too. i use happy frog mixed with perlite @ about 3:1.