Writing in the UICR area

[komuro]

For manufacturing reasons, 0xFF is written to the UICR area before startup.
Is it OK to write 0xFF to the UICR area?

[Hung Bui]

Hi Komuro, 

Could you let me know where exact in the UICR you plan to write to ? And what exact you plan to do ? 
The user area in UICR by default is all 0xFFFFFFFF (after erasing UICR they are all 0xFFFFFFFF)

Note that once you change the UICR to something else, you would need to erase the whole UICR if you want to modify the same location that you modified (You can only write once to a location)