MCUXpresso IDE does not provide specific user interface when it comes to flash security but you can do various configurations using the flash configuration block. Please inspect the Flash_Config object from the SDK source files. It's being placed at address 0x400 inside the image and it helps controlling various protection/security aspects of the MCU's flash. More details about these can be found in the MCU's reference manual, section Flash Memory Module (FTMRE).
Please note that misconfiguration of the flash module can easily lock the device.
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