You can do this in: Divinity Original Sin Enhanced Edition\Data\Public\Shared\Stats\Generated\Data\Weapon.txt.
You can get the file by extracting the Main.pak with Norbyte's tool (
EE pak extractor) or, after downloading/installing the Editor, from: Divinity Original Sin Enhanced Edition\Data\Editor\Templates\Stats\Shared\Generated\Data\ (not sure if Larian finally made the files accessible for GOG users as well) or you can get the file from the source Cadmus88 provided in this thread:
Editing companion starting properties.
