回复：NIW 求教（有关换工作， 真头痛！），恳请专家解答！

If you file your I140 (NIW!!! ) by yourself, your petition is not sponsored by your employer, then you can change your job at any time and needn't change service center. I have friends who are in same situation as yours, one of them has got green card.

Remember you only can change job at same category!