On theorytabs I find myself doubling/halving the lengths and tempo of the whole project, e.g.:
https://www.hooktheory.com/theorytab/view/rebecca-sugar/drift-away---steven-universe
The tab was originally in 3/4 82 BPM but then I changed it to 6/4 167 BPM. What I had to do was change the meter to 6/4, double the length of all the chords and notes then update the tempo, which takes quite a while. I’d like a feature that doubles the tempo and length of the whole project quickly