Since you mention git, in the past I’ve worked around many Studio bottlenecks such as the one you describe by authoring entire courses directly in OLX, version-controlling the source in git, then simply reimporting the course when needed. This works nicely because reimporting a course will basically just overwrite everything.
There even used to be a graphical way to point a course to git repository and reimport it straight from there in the “system dashboard”, but the dashboard itself is gone now (plus, it never really worked very well). But there is an API to do imports. At the time, we wrote olx-utils to do it remotely, as well as allowing some DRYing of the XML with a template engine.
Addendum: you could configure a git hook to publish a course whenever there is a git push, effectively turning publishing courses into a continous deployment flow.
Addendum 2: you can check if any of this would work for you by exporting a course into a tarball from Studio, extracting the OLX, making the changes you want (presumably to subtitles), tarballing everything back, then reimporting. If you get the desired results, then this would warrant further investigation.