I'm going to answer my own question. I used a script from redefinery rd_compsetter (which I already had installed0 which automatically adjusts various comp settings for selected master comps and any nested pre-comps.
There is no need to "correct" anything. AE is based on genuine time math and setting a different FPS in a parent comp will sample all sub-comps at the same framerate. There is no requirement to change anything in the sub-comps unless you run into issues with e.g. motion blur due to the different shutter duration. Conversely, changing the framerate of a pre-comp without adjusting the parent comp would achieve nothing. The point is not so much to change the framerates of all comps - which of course you can still do - but rather to set the FPS at the right positions in the processing chain, i.e. the parent comps actually used for rendering or even the render settings. Depending on how complex your stuff is and how many comps you have, scripts can help to adjust these things, naturally, but on an abstract idealistic level they should not be required in your scenario.
The live-action footage is the only sticking point. Going from 25 to 23.976 fps can get messy.
If you don't mind the subjects in the video moving in tiny fits & starts every so often, Mylenium's solution is the easiest & most straightforward by far. You can try it on some existing comps to see what you think. Make sure there's good motion in the live action clips so you can make a good judgement.