Per request here is the instructions.
install the program when it asks if you want to backup your PFF’s say YES
It will create a folder DXF2 Backup and place these files in there
ghw.txt
language.pff
localres.pff
med.pff
prefs.med
resource.pff
dfx2med.exe
These are your original files and you will ned them to play reg DFX2
So you can now play DFX2 BO Mod but if you want to play the orginal you need to move the new files
ghw.txt
language.pff
localres.pff
med.pff
prefs.med
resource.pff
dfx2med.exe
Out of your DFX2 root folder and the backup ones in and you can play.
Reverse that back so you can play the mod
Hopefully they will come up with a better way.
Other option is copy and paste your DFX2 directory and install the mod in its own directory then you can have a shortcut for both.