How frequent can one change jobs on approved I140

Hi,
I have an approved I140 and I plan to change my job. I know that once we have an approved I140, it is advised to wait for 180 days to change jobs. But does this apply while perm by a new employer is under process? For ex, say I move from my current employer A to employer B. Company B does my I140 transfer but perm is under process. At this stage, I140 is still tied to employer A? Can I change job before perm filing is over with Company B and move to Company C? Is there any risk I should be aware of?
Thanks a lot.

PERM and i140 are tied to a job and the company.