Hey @Neal,
I’m really sorry to hear about this loss of custom work 🙁
There is indeed a way to prevent this from happening, which is WordPress’s excellent “Child Theme” feature → https://codex.wordpress.org/Child_Themes
If you make a child theme of the parent “Divi” theme, and then add your customizations into this child theme, then you can update the Divi theme without affecting the code within the child theme.
Check out the article above for more information on how child themes work, how to make one, etc.
I really hope this helps! Let me know if that’s the case and/or if there’s anything else I can help with.
Sincerely,
George