I think I need an example to really understand what you are looking for.
In general, I let my son leave a task, then after he's calmer, bring it up again. So he can't get the lego dog look like the picture. After he's calmer, I'll ask if it matters that the dog is all one color, or if it could have spots (if the problem was not enough red blocks). So then he can know it's ok to walk away from something to regroup and go back. I do that myself. My son knows that if I quit working on something, chances are I'll go back to finish it. It's not always necessary to work straight through to the end. Taking a break is just taking a break.
Doing something for him I avoid, unless he was doing something for me, and the end result is critical (time sensitive, or has to be a certain way). Only then will I take over. And I explain why, too.
Hope this helps. If not, give an example, please.