FWIW I sent back a Dinky to JAX before PCE with an open charm and they accepted the return. It was one of the smiley face emoji plastic ones. I did make a note on my return slip that I would have accepted any other charm but those kind. This was before I knew about going into the boutique to exchange the charm.
I honestly don't see how they can refuse the return unless it's stated in writing about the charm. As long as the tags are still attached to the bags and in new condition, it should be returnable.....[emoji1]