Sad to see there hasn't been an answer to this yet. I found the same in bbw.arc but it doesn't appear to manipulate damage/charge/stamina for the skills. It's more related to the effects.
I did find in game_main.arc under param the bow_act_param08.bap.txt which has a struct type definition governing exactly what we are looking for. Problem is there's no xml to manipulate using it, just the .bap and I don't know what to do with it.
I'm guessing with some clever hex value reading one could figure out what to change in the .bap file.