sooperdood3

i just got this car used(1996 formula). i think it has a performance tune on it because it won't activate any readiness monitors and it won't pass emissions. my mechanic told me that i couldn't get this ECU reflashed and i needed a new one, so i got one, which will get a stock tune done on it at the dealership. the new ecu says it requires the PROM from the old ECU to function.

my question is can i reswap ECUs after the emissions test to keep my custom tune?