It is possible to create an override for the edit params layout only for the com_content component.
In general the JLayout system will search for overrides in the following folders, with priority order as shown:
1. templates/mytemplate/html/layouts/com_mycomponent
2. components/com_mycomponent/layouts
3. templates/mytemplate/html/layouts
4. layouts
There is a thorough presentation of the new JLayout here.
Below I will describe how I did this override, since I also needed to override the edit.php template for the com_content.
First you will need to create a new folder for the custom layout overrides. I would choose to create a folder named "overrides" and put it in:
administrator/templates/isis/html/layouts/overrides
The JLayoutHelper:render method will first search inside this folder when looking for the joomla.edit.params layout. In order to load it, you will need to keep the same structure inside the overrides folder. So the params.php file should be placed like: /overrides/joomla/edit/params.php
Then, you will need to create an override for the edit.php template file of the article view, from which you will call the custom layout.
Inside the html folder of the isis temlpate, create a folder for the com_content overrides, name it "com_content", and then a folder for the article view's template files, named "article". Copy the edit.php file from the component and drop it in the article folder.
Now, inside the edit.php, you can adjust the JLayoutHelper::render method and pass to it a new base path to look for the alternative layout like below:
<?php echo JLayoutHelper::render('joomla.edit.params', $this, $basePath = JPATH_ADMINISTRATOR .'/templates/isis/html/layouts/overrides'); ?>
This will look for a params.php layout, inside the :
administrator/templates/isis/html/layouts/overrides/joomla/edit folder.
You can keep things simpler if you just place the params.php inside the overrides folder and call it like:
<?php echo JLayoutHelper::render('params', $this, $basePath = JPATH_ADMINISTRATOR .'/templates/isis/html/layouts/overrides'); ?>
Finally, remember to also add index.html files inside any newly created folder.
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