K thanks!

This works by editing the base values for damage etc of the weapon, and doesn't alter the way the game handles upgrading weapons in any way. You should still see a change after installing this mod, even if you already have the weapon and it's been upgraded. If it doesn't change, you can drop it and re-add it to your inventory with the console command "player.additem xx000800 1" where xx in the item code is the number assigned to Danwguard in your load order. I won't guarantee this will work, but it's possible.

does this work even when you've already upgraded it to superior?

I'll give it a go. I'm on another play through and thought the same thing the first time through regarding the "weakness" of the bow. I'll be interested to see the improvement once I reacquire it. I'm an archer/thief woodelf so it will come in handy!