you can use you old priority date from your previously approved 140. it will make your case faster. but not sure as you have a pending i-485. i dont know your situation, but dont you file 485 once your date is current. also if you have your 1-485 pending for more than 180 days you can invoke AC-21,and  you can switch employer and still continue with the green card process provided that you are in similar job as your labor was filed.

or you can start filing a new labor for EB-2 category, but the thing is that if you file for the same position(and same company) it will be hard to prove that the job requires a masters degree during 140 stage as USCIS may ask you how come the same job requires a master's degree now.

These are my opinions and I am not a lawyer. you should better consult a lawyer. My lawyer were a great but they are in Massachusetts. Very experienced but a little bit expensive.