Hey there....

The way that I have accomplished both of the things you are describing in the past is to use one, or both of the following:

1. To insert additional "substyles" in your song, right-click on any bar **number** & select "Define c/d". The Style Select window will pop up enabling you to select/add any style on disk with the feel/time signature that you are looking for. You will now see that when you right-click on a bar number in the usual fashion to define "substyle a" or "substyle b", there is now a "c" & "d" available.
There will also now be a new option available to "Define e/f". You can keep adding "substyles" in this manner up to a maximum of ??? (meaning that I have only ever gone as far as "g/h").
and/or
2. Right-click **inside** the desired target bar (where you want the change) & select "Bar Settings". The pop up window will offer different options to insert (at **that** bar number) Style changes & Time Signature changes, along with a lot of other options.
Note that most of the changes you make there remain in effect for the rest of the song unless/until you perform the same procedure in a subsequent bar changing it back (or to something else).
These changes get saved with your song.

There may be better ways to achieve your goal, but this is what I do.
Creating/editing/saving your own user styles is a whole different tutorial (and usually involves a bunch of trial & error, for me confused )

Good luck!
Ciao,

Rina
<3

"When the going gets weird..., the weird turn pro."
-- Hunter S. Thompson