What is the recommended way to reproducibly override an administrator layout?

Question

I need to override an administrator layout, and the override needs to be easily reproducible in different Joomla installations. Currently, we are using extensions to achieve reproducibility. However, my understanding of template overrides is:

• They must live in a template
• Only one admin template can be active at once

Due to the second restriction, it seems I can't just create an empty template and put the override in that.

The override works if I place it inside the default Isis template, but I have concerns with this approach:

• The template could get updated. This question suggests this shouldn't be a problem, but we are still trying to avoid modifying the default Joomla code as much as possible to avoid problems with upgrades.
• We may want to swap out the backend template in the future. Ideally, none of our custom code would be tied to it.
• Doing this adds extra complication to the installation process.

What is the recommended way to reproducibly override an administrator layout? Is modifying an existing template the only way?

Answer 1

In Joomla 4 (3 is likely the same) you create a html folder in the template and inside that you create override folders html/com_thingy/tmpl/default.php, or html/mod_thingy/tmpl/default.php, and variations on this pattern. These files are not affected by Joomla updates and can easily be added to multiple sites.