If you want the memorandum to apply directly to your Strata plan, you need to adopt it under a special resolution.
However even if you don’t do that and someone challenges an EC decision that has been made based on the Memorandum, they are going to find it hard going with any SCA (formerly ISTM) strata manager, as well as at Fair Trading and the CTTT, because these bodies were all party to the formulation of the Memorandum and at the very least will use it for their own guidance.
That said, the document is not absolutely definitive even if you do adopt it because a) it’s not part of strata law and b) by-laws are inferior to other laws. So if, for instance, the Memorandum says the OC isn’t liable for damage cause by the failure of OC property but common law says it is, you might have a Memorandum-based decision overturned in a court of law. The question remains, wouldn’t it be easier and cheaper to just accept the principles in the Memo and insure your property appropriately?
There is a lot of common sense and clear thinking in the Memorandum and I would urge OCs to adopt it pretty much wholesale. But it’s not strata law so there will inevitably be disputes.