Does it work if you export the part of the song to a midi file, load the midi file to a 3rd party midi editor or DAW to change the time signature, save it, then import the midi file back into the song?
Also, come to think of it - didn’t they introduce a cut time / double time feature to the footswitch settings? I can’t find the actual documentation to it but the 3.80 firmware announcement alludes to it in the Midi Maestro support