The addresses for the eight custom characters have redundant addresses due to 'foldback memory addressing'.
Addresses 0x00 <--> 0x07 (0 <--> 7) are the primary addresses and addresses 0x08 <--> 0x1F (8 <--> 15) are the foldback (redundant) addresses for the same eight characters.
Perhaps you can use this feature to solve your problem if the Arduino compiler will permit it.
Don