Hi there @ksaltik,
If you’re using the plugins legacy reader mode theme then yes, it’s possible to edit these templates to suit your needs. To do so you need to copy any of the template files which you wish to edit into a newly created folder titled amp
in the root directory of your active theme. The files in this folder will overwrite your legacy reader mode theme.
For mobile I will use Gutenberg Editor.
Do I need mobile theme switcher plugin for this
The content shown within your reader mode URLs will display the same content as your canonical (non AMP) URLs. If you’re using the default WordPress editor (Gutenberg) this applies to both your AMP and non AMP URLs, you don’t have to do anything different for your AMP content.
You also don’t need any mobile switch plugin. If you’re happy with how your legacy reader mode AMP URLs performs you may wish to ensure all mobile traffic is directed to the AMP version by using the plugins mobile redirection option.
Rather than selecting and using the plugins legacy reader mode theme have you tried reader mode using any of the AMP compatible themes? If you like how any of those themes look or operate you can use the same themes and upgrade to transitional or standard mode.
Let us know if you have any questions with the above.