How to delete aircraft hex 053977

[TencentSZ]

053977 is an invalid aircraft ICAO hex code, and some countries' air forces use it. I tried to delete this aircraft from the standing data maintenance website but it failed. I first type in the hex and click on 'Delete Aircraft', when I try to save it, the modal says 'PNC-0256 is not a valid registration'. Then I switch to edit mode to clear the registration and switch back to delete mode, it says 'ICAO has not been assigned to a country', still cannot be saved.