Crab,
I have been waiting (in vain) for someone to answer your question about flight below MSA (LSALT); with regard to JAR-OPS 3 (which provides the underlying rules - even for coatguard operations), the relevent text is contained in JAR-OPS 3.365:
JAR-OPS 3.365 Minimum flight altitudes
(See IEM OPS 3.250)
The pilot flying shall not descend below specified minimum altitudes except when necessary for take-off or landing, or when descending in accordance with procedures approved by the Authority.
no more than this is required because, without knowing the circumstances, prescription would be difficult; operation manual (OM) procedures have to be submitted to the Authority for Approval.
All North Seas operators have such a procedure in their OM; it would be a surprise if the coastguard operator(s) did not have suitably risk assessed set of procedures in theirs.
Jim