Your snippet works, and if it’s too difficult to change the pending subject, I’ll just live with it.
Separate question… when I use your plugin to approve a registration, it doesn’t appear to apply a site role or a forum role. The setting in WP > Settings > General for “New User Default Role” is set to “Subscriber”, but for some reason this doesn’t get applied, and I’m having to go in manually and set that. The “participant” forum role seems like it’s applied when the user logs in for the first time? But that’s not entirely clear either, as some who’ve registered have the role, and others don’t. Any ideas?