If I were you I would just store each byte of the address (IPv4 or MAC or any other address) in the EEPROM directly, without trying to convert it to ascii text or BCD or anything else. Then your load/save code is trivially simple and just needs you to read and write the appropriate number of bytes. It's not as if you are ever going to be able to access the EEPROM without going through a sketch, so encoding it in a human-readable form achieves nothing useful that I can see.