To fix the dlc problem. You need to repatch (the clean ROM) after deleting the icon.bin file.
The icon.bin file is inside the 2.1a patch folder:
Fire Emblem If- English Translation [Chapter Patch + Menu Patch][v2.1a]\Patch\exe\icon.bin
I can confirm that this fixes the dlc problem with patch 2.1a on gateway.
Great work!
I've noticed a typo in one of your descriptions (bow turret).
Also, there seems to be an issue where names of weapons will cut off when you forge them, even though the names fit on the line previously.
Thanks for all the hard work.