This is where HUCA will come in handy, because my hunch is depending on agent OP will either be offered nothing but the option for a full refund, a very small fare difference refund, or, as others have alluded to, some proactive CS in the form of rerouting or similar. The latter is likely the most valuable outcome for OP. That being said, I wouldn’t expect to be reaccommodated on another carrier in this instance since this isn’t IRROPS.

EDIT: Just realized by “different carrier” we were talking different AE operating carrier. That indeed will be possible with a good agent. Likely too will skipping PHL as your TATL gateway altogether.