I think it might be possible. I mean, I'd have to look at a few .meta files before confirming anything, but, I THINK you may be able to make the fire extinguisher's "spray" deal damage.   The part that I kinda doubt though, is moving the Fire Extinguisher's 'spraying action' to a BZ/Tear Gas canister- though, replacing the fire extinguisher's weapon model might due the trick [that being said, the animations would look super messed up].