New units are defined at the specified path in the MMH55-Index.pak file.
To avoid any conflicts, copy the Longbowman.xdb file, modify the desired properties, and place it in a folder with the same name as specified in the path \GameMechanics\Creature\Creatures\Haven\Renegades\
Then, archive the GameMechanics folder into a Zip archive. Rename the extension from .zip to .pak and place it in the Data folder.
The game reads all files, but only uses the one with the latest modification date.