If you don’t feel 100% comfortable with somebody, male or female, then I don’t think you should let them change you. If something is telling you that you don’t like the thought of this person touching your private parts then that is completely reasonable, the why doesn’t really matter. Being changed is a very intimate act regardless of whether it is sexual for you, don’t let yourself be pressured or talked into it by this person (or anybody here); just because he doesn’t care whether he’s being changed by a male or female doesn’t mean you have to feel the same.
It’s okay to have boundaries around this and everybody’s boundaries and feelings around being changed, and who they would be comfortable changing them, will be different. Some people may only be comfortable with a partner changing them, some might be happy for friends to do it, some are happy to pay strangers, some people may be happy with any sex/ gender, some may only want the same or opposite sex, some might not like the idea of being changed by anyone else in any circumstance. All of these are okay, the main thing is to only consider being changed by someone you feel comfortable with. Please don’t push yourself to enter into a situation where you feel like you have to let this person change you because he says it doesn’t make a difference whether it’s a mommy or daddy, just because that’s the case for him doesn’t mean it has to be the same to you. Listen to what your own feelings are telling you about what does and doesn’t feel okay to you and don’t worry about what anybody else thinks as it’s really not worth putting yourself into a situation where you let someone change you and it feels wrong during or after the change. That kind of thing and the feelings of guilt/ shame/ disgust etc that can come about after letting someone do something intimate that crossed a boundary for you can be really hard to deal with and often the feelings of confusion that you feel that way when it was something you consented to can make it feel even worse, so if you don’t feel comfortable it is okay to say no and to voice and respect your own boundaries. You don’t need to find ways to convince yourself to feel comfortable with anything you’re not sure about, it is okay to listen to yourself and draw the line where it feels right for you.
Obviously that’s not to say you shouldn’t or couldn’t let a man change you, it might be something which you become comfortable with the thought of over time and as you build trust with the potential daddy in which case go for it, but if there is a part of yourself that feels uncomfortable don’t push yourself to go for it just because you feel like you should and especially not because anyone else has made you feel like you should.