Hard to say how he'll react to live prey if he's used to f/t. A lot of colubrids don't constrict fully like you'd be used to seeing with say ball pythons or boas. Lots of time they simply eat the prey live, butt first or sort of slam it around a bit...kind of odd really. Just to be safe, make sure his first live feeding is a smaller than normal prey item without erupted teeth. It won't maybe be quite enough to satisfy his hunger (you could offer two) but it will give you a chance to judge his hunting ability and ensure his first live feeding goes well.

We recently switched our daughter's 05 milksnake from f/t mice to live 5 day old rat pinks. It took her a minute to sort it out but she did very well and actually shows a much greater interest in feeding than she ever did with the f/t mice.