Could be that the % difference between the listing price you are trying to change to, and the lowest auto accept is less than the % difference that is allowed. I have not used best offer/lowest amount accepted for a while so don't recall what that % is. Might try getting rid of the best offer and list at the price you are willing to accept.
eBay isn't going to see your message, these are user boards, other buyers and sellers, not eBay employees.
