the doctrine is that only things that are 'novel' and 'non-obvious' (to a 'person having ordinary skill in the art') can be patented, and any accessible published material (among other things) is considered 'prior art' for determining this. So unless your 'one small change' fundamentally alters the behavior of the 'black box' in a novel way, one would probably say that it is not novel and pretty obvious for a person having ordinary skill in the art to emulate a slightly modified version the hardware in software. of course, vector search on music also seems pretty obvious to me. I don't actually know how this plays into infringement specifically rather than trying to patent something though.
