Just because its a lot harder to transplant later. If you let them go to long your roots will get twisted with each other and they will have a harder time getting nutes. Should you start over? No. Just transplant soon and be careful. Good luck.
Of course you can. You can mate different races in humans. Plants are no different. That why breeders are constantly punchin out new strains. Experement. Have fun and good luck.