Phew! Finally made it over the finishing line for this excellent puzzle but there are a few I can't fully parse. I didn't help myself by trying to find variations on "shot at is hooting......" in ODQ - took way too long to see what was staring me in the face:-)
6a - Principality once became undone in error in the field (6)
15a - Leaves suit with head to be altered (8)
5d - He buys back last bit of estate of foreign uncle (now dead) (8)
I have the answers and extra letters but the not all the wordplay.