I want to have the ability to change the time signature a song is played in. It would make writing several pieces easier. If possible, I would also want certain time signatures for certain parts of the song, i.e 5 measures of 5/2 then 3 measures of 9/8
9/8 is pretty easy. 5/2 is odd... Perhaps 5/4 would be easier to work with?
You shouldn't rely on the thick lines
You can't change the grid midway a song. However, using javascript you can set the grid to whatever (non-additive) time signature you want. I have posted how to do this somewhere on this forum, but I can't find it.
If you're just looking for some standard presets:
https://onlinesequencer.net/1277678
type grid=5/4 or grid=9/8 or whatever you want then reload the grid by zooming in then back out