This will need to be submitted to the database team to update the entry. How long? No way to know for sure
Yes, as long as you can hear the new control channel, the 396XT should be able to trunk it (for now). The database has this as a Phase 2 system, so if / when that happens, you will need a Phase 2 scanner to trunk it. The 396XT won't do it. I suspect they will run in Phase 1 to shake out the system before they all migrate, but that's purely a WAG on my part.
However, as noted in another thread, there is the possibility that if you are in an outlying area, you may have a more difficut time hearing the system. There is a mandate (?FCC) that strongly recommends reducing the signal levels in areas that are not intended for coverage.