My husband changed jobs about 3 months after getting his GC. Our lawyer did try to make him delay his switch but he didn't want to wait any longer (change in leadership in his old job made it unbearable to him). There is no real bad blood there, however, so there was no problem about him leaving. Our lawyer told us if ever there is a problem, it would be the issue of "intent" as in did he get the GC with no intent ever of staying at the old job? That is something that is difficult to prove one way or another. But in fact, when this whole process started for us, my husband had full intentions of staying with that job forever, if he and the new director in his office had not had so many conflicts. And we only discussed this whole thing as an issue because my derivative application was delayed (FP problems for me) and I was actually interviewed 4 months after my husband already got his GC and he was already working in the new company. The IIO asked me at the end of my interview if my husband was still with his old company and I honestly responded that he very recently changed jobs and the IIO just shrugged and said "Okay."
The only thing we need to keep in mind is.....our lawyer suggested if ever my husband wanted to get US citizenship in the future, he may want to wait 6 years or more, instead of the usual 5 years, because there is a chance he will be asked for his "job history in the last 5 years" and if the interviewer feels that he switched jobs too soon after getting the GC, it may not look good. I think this is a gray area....there is no definite time that looks good or bad. As I said, the IIO during my interview didn't seem to think the job switch was too soon.
But as far as I know, there are no repurcussions at this point for someone like that unless there are extenuating circumstances.