This tool by Kentaro.k-21 can extract binary data from the graphics.dat file as RAW data files and then build new graphics.dat files from extracted and modified RAW data files.

Tool-DM2LowLevelGDATMaker.Rev0.rar
- Dungeon Master II low-level graphics.dat maker Revision 0
Tool-DM2LowLevelGDATMaker.Rev0.src.rar
- Dungeon Master II low-level graphics.dat maker Revision 0 (Source code)