How to stop updates from overwriting custom templates

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   Keeping vendor and third-party templates staged separately and re-copying them after the update
2. 2
   Clearing out stale ADML files in the language subfolder to avoid mismatched pair errors
3. 3
   Using a code injection plugin
4. 4
   Creating a child theme
5. 5
   Dropping a standalone PHP file into a must-use plugins directory

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.