yes you can. check USCIS website they have full details on supplement j. have you applied for an EAD? If not, I would highly recommend you apply for one ASAP. in the future, you can also use the Ead to shift employers while your green card is being processed

you can file 485 J after 6 months of filing of the 485. few things to note - 1. your new employer needs to be able to sponsor visa H1B and if you have any remaining time from your prevously held H1B (if you did) you should consider that as first preference . once you have started work with the new employer they need to file 485J. 2. plus 1 to JDs question above - you will need an approved EAD (C09) to be able to begin work with new employer. if you had previously applied for EAD use this as an option (and if you didn’t have H1B earlier this may be your only option. 2 items that could be concerning - once you activate your EAD and use that to get employed , you have moved from a non immigrant visa (L1, H1B) to EAD. you will be unable to leave the country for international travel unless you previously had an approved I-130 (AP). if you didn’t I’d recommend you apply for that so that gives you flexibility . 3. also remember in case (by any chance ) if your 485 gets denied , that automatically results in your EAD to get revoked and you are out of status - you need to leave the country . this may be a rare occurrence but the impact of high enough if/ when this happens that lawyers usually recommend to continue on L1 , H1B status and move to EAD only when really required . I don’t see that happening given you already have an approved I-140 but you never know especially given USCIS is mandating interviews and adding extra scrutiny to all applications. 4. if you are switching employers, ensure you do so AFTER 6 months have past from your I-140 approval. 6 months after I-140 approval, an employer can’t withdraw the I-140 petition .