Right now, changing other people is a very complicated skill for the MC. Changing himself is easy because it's his own body, fully under the influence of his superhuman nature. But for others, the natural tendencies of the body are hard to manage without fucking up everything.
Giving his own appearance to a willing person was one thing. Changing a willing person (the inmate in question) into the opposite gender was another, likely successful because they actually deeply wanted it (I'm not gonna go into details but basically in the ballpark of that person being trans so the subconscious and body didn't reject the change).
Changing someone not willing, or not fully embracing it at least, is likely to cause complications that could lead to horrible outcomes.
And I doubt the MC is willing to take the risk of maiming friends just for a fuck-session. Plus there aren't any guys amonghst his friends who'd want to do that, pretty sure.
