> Resource packs can change the music played by discs. The duration of the music disc stays fixed even if the audio is replaced

You can change the music disc duration with data packs since Minecraft: Java Edition 1.21, you can even add new music discs definitions without replacing any of the vanilla music discs.

I know that one of the rules was "no data packs", but hey, it is a cool thing if someone doesn't know about it. (also, in my opinion this wouldn't break the "no data packs" rule, because the "no data packs" rule seems mostly related to not using data packs to set blocks in the world)