I met and conversed with Peter many times. He looked after my disabled wife at a festival while I was on tour in Scandinavia.
Firstly I'm very pleased that you have taken the time and trouble to listen so closely to his singing.
I would say that most if not all his delivery was taken from the East Anglican tradition, however he was a great fan of Paddy Tunney, and we talked about him a couple of times. He had a huge vocal range(On board a 98!) and a unique delivery. He was not interested in anybody copying him, he would always guide you to the tradition.
I do remember him referring to a well known singer by name and saying, 'He sings as if he's never heard a traditional singer.' To Peter Bellamy that was a sin.
I think some of the examples you have quoted are stylistic variations to help in the story telling. An old Dorset traditional singer once told me his fathers rule. 'Emphasis makes a song boy!'.
Within the British singing tradition structural variation of the melody is an accepted technique, and sometimes can result in a virtual re-composition of the tune . Listen to Caroline Hughes for a good example, however other singers like his good friend Walter Pardon do not use it at all. The rest is down to musical taste. Bellamy is an acquired taste to some people, a complete turn off to others. He was bursting with talent and is sorely missed.