Someone trying to be "helpful" pre-programmed a 12F675, but in
the process wiped 0x3ff. I've tried to re-programme the RETLW
that should be there but with no success

Tried
 
- various 'Settings' of the PIC Start Plus

- RETLW with an 0x03ff ORG
http://support2.microchip.com/KBSearch/KB_Ticket.aspx?ID=Tt6UJ9A000JWM

- searching for the "Calibration Window" mentioned in the PS+ Help

- writing 0x3480 in Program Memory before programming

Is it at all possible to re-instate a RETLW at 0x03ff ?

http://support2.microchip.com/KBSearch/KB_Ticket.aspx?ID=Tt6UJ9A000IY7

"There is a function in the PICkit GUI to force a value into that location"

The PIC in question is SMT on a board I'd rather not hack about. The
program actually runs OK if I don't CALL 0x03FF (as you'd expect -
calling ADDLW 0xFF at the end of memory is unlikely to work)

TIA

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