mirrored arms

To anyone who can help me.

I added a weapon to the back of my character for when it's unequipped and the weapon is throwing off my mirrored arms. I even put an asset I painted on the front of my chest piece and it screwed up the mirroring too. I recently saw Mm do the trick of hiding a mirrored cube to tell the puppet that there is a mirror there now but when I tried it, it didn't work. Would anyone have any ideas?

Thanks!