The same goes for me. I tried to change the names of the characters (names.dat JAP 16 kb, USA 12 kb) via HEX editor. First I looked for the very start and ending points in START.bin with the JAP names.bin as guide. Found the places, cut them out und replace it with the code from USA name.bin. I got a flashing white Screen after the "NIS America" logo. I think working with the editor is a dead end.
We should ask the guy for help who made the NISUnpack.jar. Maybe he has the right tools to repack .dat files (if he can decompress und decrypt those files he should be able to put them back together).