For developers:
I made a tool to unpack / rebuild Falcom PSP ISOs with correct LBA.
But there are packed files in USRDIR\data\cclm\map4 (*.mc1 extension) that the game will preferentially read. If you delete the entries for X####X.bin in those *.mc1 files (change header bytes to 0x00), it will read the backup copies in USRDIR\data\scena.
Link to tool:
https://heroesoflegend.org/forums/viewtopic.php?p=3034#p3034
Requires Python 3.
Usage:
1) Run unpack by drag+dropping your ISO onto _extract_new.bat
2) Modify contents of folder ISO as needed
3) Rebuild by double-clicking build.bat
This tool unpacks and rebuilds ISOs so it produces a lot of writes. Not recommended for solid-state drives.