In my experience as a teacher (and paying my way through college as a school custodian) the vast majority of administrators wouldn't know how to turn on a
microphone if their life depended on it. Furthermore they love it when a qualified staff member says "let me take care of the tech". They also hate theft and hate being hit up to pay for things to be replaced. Most I have worked with are happy to let the staff member secure the place better, especially if it means they don't have to know anything. All custodians have a key box and if that administrator or another custodian needs access it's available through the key box. As I said before you make sure the lead day and night custodians have the key. True, this means it takes a few minutes to find the right custodian, but it's not THAT much harder to get access. In general people in schools don't like to be responsible for expensive things. Re-keying is a great way to take the pressure off a lot of people and start over. There are ALWAYS students who have stolen a set of keys and gotten themselves a master key. It's better to be a little less convenient in access than have someone steal your best gear.
While we are on the topic, I've fought very hard to get the custodians to NOT let any student into the booth. True you may be my most trusted student. But it's far to easy for another student who knows nothing to fast talk his way into the booth too. I could go right now to just about any school in the country and fast talk my way into their booth. In most cases the custodian would leave me alone and let me "do my work" so they can get back to theirs. It's far better to have a policy of no one get's in without Mr. Smith or Ms. Johnson being present policy. It's way to easy to get ripped off... I know it happened to me and it was not fun.