It's interesting the way this thread has turned. I think the quoting of Article 33 is of some interest but doesn't in any way imply it's acceptable to fly non-published procedures. The article simply says that you must be at or above MSA
OR in sight of the ground - it's not a complex concept. The bit about taking off and landing is a 'red herring' in this discussion - of course you have to be below MSA in those phases of flight! How else could you land and take off? That is an entirely different concept to descending below MSA - in IMC - without any assurance of terrain clearance.
If we want to quote Articles I would venture this is a more relevant one in the context of intending to make an unpublished instrument approach, and the one lawyers would be most interested in:
Commander to be satisfied that flight can be safely completed
87. The commander of a flying machine must, before take-off, take all reasonable steps so as to be satisfied that it is capable of safely taking off, reaching and maintaining a safe height and making a safe landing at the place of intended destination having regard to—
(a) the performance of the flying machine in the conditions to be expected on the intended flight; and
(b) any obstructions at the places of departure and intended destination and on the intended route.
The topic of mid-air collision has some basis I guess, but it would be a shame to allow it to distract attention from the real reason this thread is important. Hitting the ground is the most likely danger - not another aircraft. Probably even less likely given that we are talking in the main about modern medium twin IFR helicopters that will generally be ACAS equipped.
One point of clarification - when I say published procedures, I also mean private procedures that may not be generally available to other operators, but that have been designed by a professional Procedure Designer to PANSOPS/TERPS standards.