I think this image should explain what I am trying to achieve.
Basically the accessory is fine on R6 rig, but are rotated on R15. This is because someone thought it would be really funny to change it’s orientation from 0, 0, 0 (like on R6) to -90, 0, 0.
I need a way to maybe use one attachment for R6 avatars, and another with R15. I just have no idea how to swap them.