If you want to slow it to 24fps, you can slow the audio down by encoding it like this:
ffmpeg -loglevel error -stats -n -i “The Wrong Trousers HD v2.mkv” -vn -sn -af asetrate=46080,aresample=48000 -c:a aac -b:a 192k -vbr 5 “The Wrong Trousers HD v2.mka”
And just remux it with the video in mkvtoolnix, de-selecting the original audio, and setting the video frame rate to 24fps.
I’m not well versed in ffmpeg, does this operation keep the correct audio pitch? I assume you’re posting this for the benefit of those who want to keep their file BD-compliant.