Cubase 10 lets you create different “track versions” for each single track. All the different “Track versions” are saved in the same Cubase project so you can easily compare how your whole project sounds with the new track version, against your project that uses the old track version.
But if, for example, I change all my midi tracks at once by putting an extra bar in the middle of my project, can I still audition and save both the old and new tracks version within the same project? like I can do for single track versions?
I don’t know the answer for certain off the top of my head, but I’m pretty sure the inserted bars will show up in all versions of the Tracks.
That said, you can easily find out the answer for yourself in under 2 minutes by just giving it a try (which is what I’d need to do to give you a “certain” answer). 
Save before trying and if things get messed up you can revert to the saved copy.
Or if that seems too risky use Save As to make a copy you won’t care if you mess up - or even create a Project just to do the test (for most simple stuff like this I go the revert route).
A lot of folks seem reluctant to simply try something and see what happens - which for many questions will give you an answer much faster than asking here. You won’t break Cubase by trying stuff. And you won’t break your Projects if you take a minimal amount of care ahead of time to have a clean saved copy of the Project.
I tried it - if I add a bar it affects all track versions. My problem is a bit different - I will rephrase it.
Regarding midi tracks: I can have different track versions for each of my midi tracks in the same project. This is useful.
But can I have different versions of all midi tracks taken together? My Cubase 3.6 let me do this, and the versions were called song “arrangements”.
If I understand your question correctly, then yes.
What you want check out are Version IDs.
When you create a New Version of a Track by default it is given a new ID number. These are just 1, 2, 3, etc. in the order created. But if you create a New Version of multiple Tracks at the same time, they will all get the same ID number and you can set Cubase to change all the IDs that are the same at the same time. Not at my DAW for how-to specifics but it is pretty straight forward and in the OPs Manual. You can also edit the ID Numbers after a New Version is created to get them to match - but that’s much more tedious that doing it at creation.
I have been reading the Cubase manual on this with some difficulty and am still trying to get it to work. It is very longwinded compared to how simple it was in Cubase 3.6.
Have you tried searching for videos
https://www.google.com/search?q=cubase+track+version+id&sxsrf=ACYBGNSc7oJJkMIZOK3Qv9rPYu4g2FCftg:1573244036992&source=lnms&tbm=vid&sa=X&ved=0ahUKEwjO7eDfttvlAhVSXK0KHQofAbwQ_AUIEygD&biw=1704&bih=914
I’m pretty sure the answer is no if you are asking if you can compare pre/post adding a bar. That is a separate protocol outside of track versions I think.
I had a similar question and thought when I was editing dialogue the other day. We did some re-records of a section of dialogue and we wanted the voice over artist to do this part a bit slower. Having been in a ‘TrackVersion headspace’ already, I made the mistake of staying in that head space and doing ‘Duplicate TrackVersion’ and creating new empty space in the project for all tracks (which as you found, adds space/time across all previous track versions).
I wanted to go back and compare, but then realized, wait a second… this is actually super confusing.
So I came to the conclusion in this instance, that I should have either:
A.) Duplicated TrackVersions across all tracks but then copy and paste EVERYTHING over to the right shifting it to the far right of the Cubase project into empty unused space, so essentially, there are two copies of the same project across the timeline of the Cubase project. then I use one of those copies to create a new version I am adding new space to. (if you have automation, turn on, automation follows events so it moves with the copy)
or
B.) Sort of the same as above, but just putting the entire project into a FolderTrack and duplicating the FolderTrack so that one folder will be kept as the old, and one folder contains the new in which instead of “insert bars”, I use ‘insert silence’ with the range tool across only the tracks I need to add space making sure not to range over the old folder, only the new. you could lock the contents in the old folder to as well to be safe, I believe that will prevent insert silence on the wrong thing.
lovegames-
B, above, looks a possibility I can follow. Put ALL tracks in a folder, then duplicate it in another folder.
Why oh why did Cubase get rid of midi project arrangements? It seems crazy.
There’s the Arranger Track? you could potentially use it as a method of ignoring the new bar you created so that you can listen to the old arrangement.
Yes, but it is awkward, because I often shift all the tracks around, not just adding a bar, when making a new arrangement. I cant believe Cubase got rid of arrangements.
How do you mean, shift the tracks around?
What version were MIDI arrangements in?