Currently, the only way to modify settings values in Secure/Global tables is to either export a mini plug-in via App Factory and grant that app this permission, or to the the AutoTools plug-in.
However changing device settings seems like such a fundamental feature that it should be made native to Tasker. Tasker already lets you change many device settings, but there's no way for it to account for every possible setting from every possible device, so let the user manually choose.
Right now, just adding the permission itself is enough. It might mean we have to use a clunky Java command to actually modify settings, but eventually you could revisit and add an interface for changing Secure/Global values.