Is there a way to activate different theme for specified users? [closed]

I’m looking to allow beta testing of a theme on WordPress site in production.

I was thinking of a plugin to check if WordPress user has been selected for beta phase, and if this evaluates to true then activate another theme for him/her.

Ideally users could opt-in/out of beta phase by just visiting their profile. Admin of the site would then select the desired theme.

Any suggestions?

This is rarely as simple as it sounds as new themes usually require some adjustment of the content (different image sizes? different menus?) and maybe new plugins or setting changes. It is not impossible, but the work required to actually be able to do it is different from site to site.

Of course if all you do is CSS changes it should be easy to add a setting to the user’s profile and add the relevant css file or rule when the specific user views the site.