I installed and activated the jonradio Multiple Themes plugin.
I created a new page and published it.
I went into the jonradio Multiple Themes settings and under:
For An Individual Page, Post or other non-Admin page; or a group of pages, specified by URL Prefix
...I selected a theme from the drop down. Then I pasted the full URL to the new page.
Then I clicked the Save Changes button on the jonradio Multiple Themes Settings page. The page refreshed and did not advise at the top that the changes had been saved. There was no message of any kind (success or failure). And after the page had refreshed the theme I had selected was not selected and the URL I has pasted was gone.
So I selected, pasted and saved again. Same thing.
Next I went and checked the page URL I had pasted in the Settings. The page was blank except for a message that there was no config file! And there was a button to fix things--I did NOT click that. I thought, "Oh great I've jacked up my site with this plugin." So I hit the home page and other pages and they work fine. I double checked the page I had specified in the settings and it gave me the same message.
So I deactivated the plugin and reactivated it. I repeated the page assignment process but this time I assigned a page that had already been on the site. The page worked with the alternate theme.
The problem is the page was a mess now because this alternate theme has many custom settings as does the active theme.
Is there a way to establish all the settings for the alternate theme so that it can be used on one page? And is it possible to do this without messing up all the settings on the main, active theme?
This question applies to the menu and page layouts also.
Thank you for the help. This is a very rare plugin for what would seem to be a common issue--people wanting to use more than one them (and menu, et al) on a single site.