I tend to only heat with steam once, when the moisture content is still a bit high, and I do the entire bow. I leave it alone then until it's dry enough to begin working on, and then if another correction is needed during the process, I use a heat gun. I have heated stubborn areas of selfbow staves several times before I got them right where I wanted them.
I love unique bows with lots of character, but there comes a point where each of us must decide when to stop torturing a piece of wood, or when one is just too twisted, crooked, or knarly to be worth the effort.