What plugin to use to quickly change customized templates?

Question

Debugging

The situation is the following.
There is a visited wordpress site with a customized template and you need to quickly and painlessly activate and configure another template.
Is it possible to save the current template settings: widgets, plugins, etc. So that in the event that the second template "does not work", you can quickly roll back to what it was.
Or maybe how to set up another template on another site, save the settings. Then activate this template on a new site and import the previously saved settings.
Senk in advance.

Answer 1

Plugin Theme Test Drive
Install, and change the theme through its settings. It will change only for site administrators, all theme settings will be available. Users will have the old theme.
When you are done with the settings, just change the theme and that's it :)
There is an opportunity to test on a local / test server, then of course you should not neglect this opportunity :)

Answer 2

It is better to do of course with an intermediate development / staging server. If everything is ok - transfer to production.
Plugins and their settings will not crash, they do not depend on the theme. The options of the WordPress itself will not fly off. With widgets and menus, there can be nuances, since they are tied to the theme (sidebars and menu areas are defined in the theme). By itself, your menu will not disappear, but you may have to reassign it to a new area.
As for widgets, at the very bottom of their settings page there is an area for saving widgets with settings. Move them there, change the theme, and then return them back - stuff them into the right sidebars.