This sounds like you have a KX15DTAM anti masking detector. The flashing blue LED tells you that it is processing the anti masking to confirm that the detector hasn't been partially or fully covered over so this seems like normal activity. You can disable the LED but be aware, if you do so, you have no visual verification that the sensor is operational. If you do have a fault on the sensor, the alarm should display a fault on the panel or fail to set.
To disable the PIR I would recommend entering engineer mode first. If you don't have an engineer code, you will have to silence the tamper alarm with your user code once the detector lid has been removed. Depending on how your panel has been configured, you may require an engineer code to reset the tamper after so bare this in mind. You will find a bank of dip switches on the sensor once the lid is removed. You will need to switch jumper number 1 off to disable the LED.