You need to be able to modify the contents of the disc, which implies that either you have managed to boot your own OS or you have been able to temporarily plug

You need to be able to modify the contents of the disc, which implies that either you have managed to boot your own OS or you have been able to temporarily plug the storage into something else. This is as you say a much lower bar to clear than modifying the OS of the device as in a classical evil maid. Effectively, the maid is already built in to the OS in the form of the bug.