sisemen
Since WWII the registration requirements for military type operations carried out by civilian organistaions has evolved more than somewhat.
In the late 60s/early 70s the CAA were totally happy for HSA to civil register a Harrier and fly it to a country that would not accept a military reg for example. Then in the way oganisations like the CAA evolve they became unhappy with this or that being done under the ANO and eventually a dual military/civil reg system such as that used today evolved.
Mind you none of this changing legislation (for legislators sakes in my view) had any effect on the safety of whatever was being done. As always that was down to the individuals operating the aircraft.