1. Is there an addon to let user's change their theme? The theme I'm using on my forum relies heavly on modified files from the themes directory, not just the css files. But I'd also like user's to have a choice when using it, so they can revert back to the original.
2. I'm not quite understanding the theme layout for having multiple themes:
/themes/vanilla/ /themes/My_theme/ would be in the same themes directory correct?
1. I did search, but the "theme changer" in there relies on having the vanilla.css file in the directory. I'm talking about changing the theme template files not just the css.
Yes, that's because the styles are in subdirectories of the theme directories. /themes/ is a directory where all themes live, so yes, vanilla/ and My_theme/ would both be in /themes/. Under each theme you have a style directory where the styles for that theme are stored. So if you want two different themes, but the same style, you'd need to copy the style directory from /themes/vanilla/styles/yourstyle/ to /themes/My_theme/styles/mystyle/
The theme switcher is only for admins, but I guess you should be able to modify it to work for any logged in user.
By the way, I'm just curious, why would you want users to be able to change the whole underlying structure of the forum? :)
I have modified the underlying structure to fit a certain style, it wasn't possible to achieve what I wanted to do with just CSS. Some html elements were missing. So I would like it so user's can switch to a default vanilla or my changes.