Hi Howard,

Not sure how the pic programming (memory division, write protect) is done (AVR person) but have you considered putting the transponder "strings" into eeprom? on power up the program would load a string out out eeprom.
You could lock the program space but leave the eeprom space read/write allowing end users to update the "string table" (or populate it from blank).
Combined with some form of decoder, it would allow people to clone existing transponders, avoiding totally issues of clashes.

Any idea of the power required to run the transponder?