Its possible and relatively easy to fix. I just factioned an Ogre Shaman so I could bank in FP. Easiest way is to kill Orcs, which naturally give Knights of truth faction and then turn in the deathfist belts for Freeport Militia faction
https://wiki.project1999.com/Deathfist_Slashed_Belts (you want to do the evil version (freeport militia))
Initially you'll need a druid to wolf form you to turn them in until you're no longer KOS so I would recommend filling all your bags with Belts and turning them in together. It probably takes around 100 belts to go from scowling to non-kos.
Another easy quest you can repeat over and over very quickly is:
https://wiki.project1999.com/Note_for_Rebby
It spans over 2 zones (EFP and WFP) so this is a lot easier to do once you're no longer KOS so you can do it without wolf form. Be careful as there was an NPC I was still KOS to near Rebby but they didn't hit very hard so was plenty of opportunity to complete the turn in and zone out the agro. I was using this to faction with the merchants until I determined that I didn't need to be non-kos to the bankers in NFP I could just bank outside of line of sight.