It sounds like you want to upgrade the building’s common property, to manage the access to that “common property” yard area that seems to be adjacent to Lot … That upgrade seems worthwhile, and so you (and the other interested and cooperative owners) should get together and draft a suitable motion to put to a general meeting. Depending on the level of support and the building’s finances, it may be helpful to get some quotes from builders, to provide options and cost estimates. For example you could fit locks to prevent access to the common property yard, apart from authorised persons (and there are special security ABLOY locks that only meter readers and electricians have a master key, for instance). Or you could install locked cabinets just around the meters and valves. Or decide to use the area for something worthwhile for the building, like a vegie garden, or compost bins….
Your strata manager can help draft a motion, or have a go yourselves. Propose the best option, or a choice of a couple of options, along with the quotes and a budget at the general meeting of all owners. The owners can then approve, with a majority vote, but you may need to increase your levies or raise a special levy if you have insufficient funds, and include that in the general meeting motions, if so.
The second step is to review your by-laws, and amend or add some to administer that area. For example you could add a by-law that does not permit access by residents and owners and others to that area, unless they have reason. But back that up with locks, and a by-law can restrict access to the key to just office holders, or 2 strata committee office holders together, if one alone may not solve the problem.