Hi Masahiro Kiniwa ,
Do you also use the IDE to modify your app 0X40D? Or you use your programmer to modify the 0X40D directly?
I never used programmer Xeltek SuperPro750 in the previous time, so you really need to contact with the programmer company.
Do you try to modify the 0X40D in the app directly?
About the override option in AN4835, it should be doing the FOPT erase and write operation in the related flash area.
In fact, we normally modify the FSEC in the FOPT directly in the app code, then generate the related app, and download with programmer. You need to check with the programmer side, whether they have the allow security function.
Just take the JLINK as an example, JLINK as the device-ALLOW SECURITY function when select the chip partnumber.

When you select the allow security, it means you also can modify the FOPT area.
Have a great day,
Kerry
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