My 140 and 485 has been approved. I am thinking of changing jobs immediately.
---to be safe remain with employer for 6 months after GC or get letter from employer that they dont have job for you and keep that letter with you till you apply citizenship., becase if you leave immidiatly after getting GC it means you did not have INTENT to work with employer and can be seen as fraud just to get the GC through employer and having no intent to work after GC
Can my employer withdraw my I140 petition now or if they tell USCIS that I left them after I got my GC, will it have any effect?
----- yes the employer can report it to USCIS and GC can be revoked,, your will be investigated and at the time of Citizenship they will discover every info about you if you worked with the employer or not. not only employer even if your any enemy or friend informs USCIS with your full details USCIS can investigate your GC case
Once a person gets a GC, under what conditions can it be revoked?
-------- it has many reasons you can serach through google " Permanent residence or Green Card can be revoked if..." you will find the many reasons
I read that I might have problem when apply for citizenship
---YES and also at the time of GC renewal if you dont apply Citizenship they will find out at the time of GC renewal
(well that's long way so I am not bothered about that
)