I used to feed mine f/t and I went to feed live and I've seen no changes in their behavior what so ever except maybe them getting excited when I have rats and I slide out the tub and they smell the rats and get excited but other than that they haven't got any more aggressive since the switch.
It's perfectly fine All my ball pythons were eating F/T until I ran out of freezer space for the larger rats. Now they all eat live and are still as tame as can be.