I’ve added a field to the ChangeDetails struct which is passed to updateHostDisplay. By setting this new flag, the plugin can notify the host that the plugin state needs resaving. At the moment, this functionality is only implemented for VST3 and AAX. There does not seem to be equivalent functionality in the VST2 and AU formats.
Hopefully this works for your use-case - please try it out and let us know if you encounter any issues.