After contacting the Conference re the resignations/poaching I received the following reply
Dear Mr *****,
The Conference is aware of these appointments but is not party to any contractual arrangements between Clubs and Managers.
I believe this is an employment matter between the Managers and their employer, and perhaps a civil matter which Boston United FC may chose to pursue.
The General Manager
The Football Conference
So it looks like the Conference is not going to get involved.