A great answer Henrik (good spot on my erroneous write too!)

That was a top heads up wrt ....DATA @1, ""

and goes some way to resolving the confusion I have wrt managing where the written Eeprom data commences being stored! Presumably I can tuck the user defined byte (called default_config) away at the very last slot of eeprom with...
Code:
DEFAULT_CONFIG  DATA 255
& then place the other 255 bytes below that?

... I'll revisit this after the kids are off to bed, but that was a great reply & gives me plenty to get my teeth into - thanks. (PS I haven't forgot about the DDS stuff you did ...I really want to revisit that as soon as I'm finished this melarkey!)