You can change jobs; as long as the 140 employer will not withdraw/revoke the 140 before approval.
Remember greencard is for a future job. you don't even need to be with the employer when 140/485 is applied. On the safe side to prove intent, it is better to be with the employer until 140 is approved and 485 o/s for more then 180 days.
However, if you have to change jobs before, then go ahead but get assurances from the sponsoring employer that they won't withdraw the 140 before approval.
It was covered by Yates memo that under ac21, there is no need to ever have worked with the sponsoring employer before, during or after greencard was approved. That is the concept of a future job. Even with the future job, you can change intent and use ac21 without even working with the employer who sponsored you for the greencard.
USCIS is well aware of when one chages jobs; simply because people will do an h-1b transfer and it will be in your record that you have changed jobs before 140 was approved and/or 485 o/s for less then 180 days. USCIS hasn't denied any case for someone changing jobs early; they have only denied cases where employer revoked the 140 before the 180 days was up on the 485.