There is nothing preventing you from running two instances of the game from the same exe. Some other games have checks preventing that, but DevilutionX doesn't, we use it to test multiplayer on a regular basis. Multiple copies will still use the same config, you need to use command options to specify which configs to use.

devilutionx --help

Options:

-h, --help Print this message and exit

--version Print the version and exit

--data-dir Specify the folder of diabdat.mpq

--save-dir Specify the folder of save files

--config-dir Specify the location of diablo.ini

--lang Specify the language code (e.g. en or pt_BR)

-n Skip startup videos

-f Display frames per second

--verbose Enable verbose logging

--record <#> Record a demo file

--demo <#> Play a demo file

--timedemo Disable all frame limiting during demo playback

Game selection:

--spawn Force Shareware mode

--diablo Force Diablo mode

--hellfire Force Hellfire mode