Your existing 396T files will work just fine on your 325P2. I have a 396T, 396XT, and the 325P2, and share a "master" file among the three, selectively loading whatever mix of systems I want for that scanner, and/or a specific trip or event.
However, if you end up doing the DMR upgrade, FreeSCAN will not handle a DMR system. You cannot program DMR with FreeSCAN, and it will not 'save' the system correctly if you "read" the 325P2. So, if I'm loading the 325P2 with one of the local DMR systems, I do that with ProScan.
I do the same thing in Freescsn with a 15x, two 396xt's, 996xt, 996p2, and a 325. One freescan file so all the quick keys are the same in all radios, even though I listen to different stuff on each radio, I load everything into each.
You need the latest 2.18 version of freescan. 2.17 will not work for the 325 or 996p2.