Technically, you should be able to use them interchangeable and for FP+ you will...
However, based on the experience I just had the last few day, you might want to be careful. I used my Passholder band and did not get a band linked to my stay (wasteful)... Anyway, the Passholder band was completely linked in the MDX account, etc...
Well, the Passholder band first did not open my room. So, I had to return to the front desk and have them make sure my band linked to the room. Then I went over to Epcot and went to charge something and showed I had not linked a credit card (which is completely untrue)... So, I had to return to the resort and have them re-liink my credit card to my Passholder band...
It was very frustrating and they have not had a lot of experience yet with guests having multiple bands and using one from a previous (or Passholder) visit...