I will have to go back and read the resolution, or better yet, my new manual is nearby. As I recall, as long as the minister is not put under question by the district in which he left, he is able to preach anywhere in the UPC. If he is put under question, preaching him would be a problem.
As someone who values his "independence", I would find it insulting to have a board tell me I could not preach someone if he was not under question. If he was officially under question, as one who has agreed to abide by our bylaws, I would not preach him.
Doesn't mean I would like it, just means I would abide by it!