im too much of a brainlet to do that
basically don't make the belt two separate images.
just make the normal one have the mountpoint still be 2,
then use this code
function WrestlingBeltItem::onUse(%this, %player, %invPosition)
{
%image = %this.image;
%player.updateArm(%image);
%player.mountImage(%image, 0);
}
That'll make it visually appear on mountpoint 2, but be in the 0 slot.