Just FYI so you can learn about the medications you are taking (and I'm not trying to be snarky...truly trying to help as I think it's good we all know what medicine we take
) the 500mg amount is the amount of Acetaminophen in the tablet. The first number is the amount of the opiate.
So if your previous medication was Vicodin or Norco...it may have been 5mg or 10mg . That is the amount of the Hydrocodone (the opiate) and then it shows a / symbol...and then the larger number will be the Acetaminophen.
The new medication you are going to take is Percocet. This has the opiate Oxycodone in it as well as Acetaminophen and will be labeled the same with the smaller milligram first and then the larger milligram.
To answer your question...lol....You should be able to fill the new prescription since it is a totally different medication. Unless the Dr. specifically put a "Do Not Fill until x/x/xxx" date on it....you should be fine.
Hopefully you will get better pain relief...Good luck!