avrsinewave:
The bytes coming in will be miidi program change messages.
Oh, OK. I assume that defining the supported commands would be a one-time activity and you aren't too concerned about how much effort it takes.
That being the case, it would be reasonable IMO to store the mapping (from the MIDI input byte to the output states) in EEPROM. If I were you then rather than using input buttons etc to perform the programming, it would be easier to just provide a command line that let you type the byte value and the corresponding output states in via the serial monitor or whatever other serial client you wanted. It would be quite simple to implement a sketch that let you type in 'SET 55 01001010' for example to define the output states corresponding to input value (decimal) 55. If you implement this approach there is no reason to limit the number of output states to eight, and if you think there is any likelihood that you will want to support more than eight outputs I'd start now by holding the output states as a 16-bit or 32-bit int.