Would it possible to be add the ability to create a rule target which can be fired when the value of the setting (at system level) has been changed?
Example usage of said rule (if the ability was added)
You have a XML system level setting containing information on what values a bunch of specified user level settings should be set to for a set of users inside usergroups
<setting name="Location" value="Mars">
<setting name="Moons" value="Phobos, Deimos">
<setting name="Location" value="Earth">
<setting name="Moons" value="Luna">
Now, Say the Earthlings decide to move to Venus, Then we would like to update the Location part of the xml for Earthlings from "Earth" to "Venus"
When the setting is saved, a new custom rule at this point would kick off (as it's targetted by the suggestion in this post), then with some code inside a custom rule we would then change all the Users inside the 'Earthlings' Usergroup, There user setting for location from "Earth" to "Venus".
For Adam's information - this is related to request #5473
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