Hi Ian Hill,
The way I solved this issue, was by keeping the old version of File Viewer Plugin (Version 1.0.1) and adding the new (at that time) version of File Viewer Plugin (Version 2.0.4 ).
I was able to compile the app with both versions.
Then I used the "CheckPlugin" action of the new File Viewer Plugin (Version 2.0.4 ), if IsAvailable = True I used the newest version, otherwise I used the old File Viewer Plugin (Version 1.0.1) .

This way the older mobile Apps running on devices will keep using the old version of File Viewer Plugin (Version 1.0.1), and the newly compiled apps will use the new version of File Viewer Plugin (Version 2.0.4 ).
When the App is released to stores (Apple & Google), all devices will use the newest version of File Viewer Plugin (Version 2.0.4 ).