Thank you, Golden Rivet. That is a most interesting document.
The KM insisted that commanders follow the Prize Regulations from Day One, then started curtailing them about Day Two.
The fact that they were utterly impractical for submarine warfare had a lot to do with this. They were designed around the paradigm of commerce-rading surface cruisers like sailing frigates.
The mere existence of the Prize Regulations was a great inhibition on U-boat commanders during the first year or more of the war. Blair tells the story in detail. Some of the commdaners were recklessly gallant in their efforts to conform to this standard of "civilized warfare" (an oxymoron if there ever was one!). Without the Prize Regulations, the blockade might have been more effective from the outset and had more of an impact on the course of the war.
JFO! provides a taste of the stream of confusing and contradictory orders that came from KM as they wrestled with the challenge of establishing an effective submarine commerce blockade while abiding by gradually diminishing elements of the Prize Regulations. NYGM and SH3 Gen also include about 90% of this material. It is educational to read these radio messages and patrol orders and to imagine how an RL commander would try in good faith to make sense of these limits and restrict his activites in practice.