Toaster and source control

I have a couple of questions that relates to workflow in Toaster.
To me toaster is easy to work with and I see a Custom Image option.

However,I try to create swupdate rootfs image and swupdate .swu image
through Toaster.
But where do I add things needed in a custom image, like:

SWUPDATE_IMAGES_FSTYPES[core-image-full-cmdline] = ".ubifs"
I don't think Toaster supports Bitbake variables with [].

https://sbabic.github.io/swupdate/building-with-yocto.html

Should I manually create a layer myself, and add it back into Toaster? How
would a workflow like this look like?

Also: How could I work with Toaster and check the altered files into source
control? I created a project which I have modified a lot, but I didn't
choose "Merged Toaster settings (Command line user compatibility)". Is
there a way to retroactively specify this? I am the only person working in
Toaster, I just found it easy to start with yocto with it.

Thanks a lot in advance!
-- 
Emil Christopher Solli Melar