Beaming from Inspector
While it is possible to change the beaming on one line, the function does not seem to work well when selecting all time signatures for a score and altering the beaming.
For example, changing the default 7/8 grouping of 3+2+2 to 2+2+3 by clicking on a time signature and pressing "Properties" in the inspector does not seem to work.
Comments
See the GIF:
https://musescore.org/fr/node/335600#comment-1143683
It indeed only works for one time signature (there's an issue for this somewhere). The current (fairly easy) workaround is to adjust a single instance, then Ctrl/Cmd+Shift+Drag it onto a palette for reuse. Then apply it from the palette back to the score.