Is Cert Patch a Stable Solution or Temporary Fix??

I wrote a new IMEI to a G920T and I patched Cert after that. Everything is good.

But when I flash the whole firmware back, the cert is not patched anymore. the phone cannot pick up service anymore. I needed to root again and patch certificate.

I am thinking Cert Patch goes away with a full firmware flash or update. Correct me if I am wrong.

I had to write a new cert cuz it seems more stable.