Theme Rules

The Theme Rules module provides an action to switch themes. It affects a user's account, as though they changed the setting in their own profile.

Drupal 7.x

Using Entity API, Rules can natively change a user's theme. For example:

{ "rules_set_user_theme" : {
    "LABEL" : "Set user theme",
    "PLUGIN" : "rule",
    "REQUIRES" : [ "rules" ],
    "USES VARIABLES" : {
      "user" : { "label" : "User", "type" : "user" },
      "theme" : { "label" : "Theme", "type" : "text" }
    },
    "DO" : [ { "data_set" : { "data" : [ "user:theme" ], "value" : [ "theme" ] } } ]
  }
}

Background Discussions

Rules issue: #417664: Action: switch theme
ThemeKey issue: #647716: Integrate with Rules

Acknowledgements

Madhusudhan Srinivasa of QED42 is the co-creator of this module.