This happens because the OMF installation script has already set up the module for you.
If you want to change the Category Mobile module layout or add a new layout, follow these steps:
- Go to the OpenCart admin>Extensions>Modules
- Click Uninstall for Category Mobile
- Then install the module again
You should now be able to edit it.
*Please, note: If you wish to have the list of all categories when clicking on the "All Categories" link, choose
[OMF]All_categories for layout.