Is there a way to prevent Captivate 7 .cptx files from becoming corrupted after updating them and editing them with Captivate 10? Thank you.

It may be a lenghty process but worth giving try. I would rather suggest you to try upgrading the projects to cp8 than cp9 and then open with cp10.

You may get trial versions for all versions from here

Download Adobe Captivate

If this still do not work, only way could be copy and paste the slides in newer version.

t is a big jump from 7 to 10. So much has changed, and I'm not talking about the UI shift but about states for uttons, new effects, changes in advanced actions etc.. Support and focus is now almost exclusively on HTML output, whereas SWF was the primary output in 7. Did you try to create a csutom heme,in CP2017 , create a blank project with that theme applied and copy/paste the slides from the upgraded project?