Apologies in advance if this is already possible. I've scoured the wiki, github and my configuration files and can't find a way to change the quivers curios slot. I've seen other packs allow quivers in different slots but not 100% sure that they used this mods quiver to do so.
I just don't want to choose between a backpack and a quiver and value my inventory space.

Curios are handled by tags. You just need to tag the quiver with one. It's explained on their page

Also quiver can be used normally in any slot