What I intended was to write x'700' to x'10001080' i.e. NRF_UICR->CUSTOMER[0] !
When ran my application, which outputs NRF_UICR->CUSTOMER[0] to the log, I was very confused until I realized nrfjprog correctly clobbered a location in RAM.
1) nrfjprog should not accept the address in decimal (Who does that intentionally??).
2) nrfjprog should not accept a value with a leading 0 (Surely the user meant a hexadecimal value)
3) At an absolute minimum nrfjprog should respond with
writing 00989AB8 = 000002BC
Then I might at least have had a chance to notice the odd values it reported.
Thank you for you consideration.