First, to provide a bit of case history.
I adopted a mustang yearling a little under a month ago, and have been working with him since on gentling and so on. He leads fairly well, longes and changes direction decently, and has started to allow me to touch him all over. The biggest challenge right now is catching him initially. I have to sort of corner him and use a stick to rub up his body until I can hook it under his chin and move in to catch hold of his halter. Once you've "caught" him and gotten into his space, he will stand and allow you to rub on him with or without holding on to the lead rope. I've even stood there and braided his mane without holding on to the lead.
So, I'm trying to practice leaving his space and coming back into it without having to use the stick, pick up the end of the rope he's dragging some of the time, or otherwise "cheating". I've been dropping the lead rope and walking away from him for varying periods of time, then walking back to him and talking to him as I approach and reach out to catch him again. When he allows me to come back, touch him, and take up the lead rope again, I give him a small treat. I stand calmly next to him until he's finished chewing his treat, then ask him to lead in a small pattern or allow me to rub him up and down his body, at which point I repeat the whole process. As he gets better, I want to snap and unsnap the lead rope on and off each time that I leave him and come back.
My biggest question is whether it is appropriate to give him a small treat each time he allows me to come back and catch him. Am I at risk for making him mouthy? I would reward him with a scratch on the neck or a kind word... but I'm afraid he still finds those things like being touched and talked to strange and not altogether pleasant. Is there any other advice for how I should work with him?