Thank you for that. I was thinking in terms of Newtons 1st law of motion in a perfect vacuum (and over eons of time) and didn't consider that light itself has inertia and would affect its angular momentum as its being radiated. But, isn't it still conceivable that even down to the last atom of the magnet, there's a mathematical improbability that the spin would be zero, considering entropy? Or maybe the opposite is true, that entropy was working toward bringing the very last atom down to the lowest energy state possible, essentially converting any remaining angular momentum into light so that it can achieve the lowest energy state possible. I could see it going both ways, maybe even being in an entangled state of both outcomes until an observation is made.

A stationary magnet has a static (fixed) "field" around it. In a perfect vaccuum, it doesnt emit any photons, because theres nothing interacting with it that would cause it to become "excited" and emit EM radiation.

A rotating magnet, regardless of being near a black hole, produces a dynamic (changing) magnetic field, and since those interactions contain information (quanta), we're all familiar with something heating up - which are photons in a spectrum we can't see with the human eye. Given enough time, in theory, the entire mass of the magnet would eventually be irradiated outward as light energy.

Lenz's law provides details on extracting energy from this very thing. You can spin the magnet around an electrically conductive material, like an iron nail. The nail becomes excited by the photons, and electrons start moving around (electricity). Alternatively, you can shake or spin the iron nail around a permanent magnet and produce the same thing via induction.

Your question in regards to a black hole is quite intriguing. Yes, a rotating magnet can act as a broadcast antenna, but its not very efficient to do so because magnets and all ferromagnetic materials have the uncanny ability of picking up and amplifying extra signal "noise" (ingress). What's fascinating to think about, is that a magnet in orbital motion around a black hole would indeed act as a "pickup" in exactly the same way a guitar pickup works. All these frequencies being thrown around together would be picked up and turned into the electrical signal version of the EMFs, then be induced back into the magnet in a Jimi Hendrix-esque feedback loop.

So when you're saying a "magnet" is spinning around a black hole, don't imagine a handheld rectangle magnet. Imagine instead that it's a magnetar... I mean... I can't even fathom the magnetic power of one of these alone, much less being involved in a stellar dance off with the energy source of a black hole. If something like a pulsar/magnetar were to be energetically involved with each other, theoretically you could place the magnetar in an energy jet stream of the black hole, and it would emit a "fucking huge" broadcast signal of their blended frequencies... may I say, "spacetime modulation?" Hmm...