Thanks for seeing through my misleading terminology (on 'groups' and 'membership') to provide the above pertinent workaround!
What I'd like is a seamless extension that runs such SQL queries behind-the-scenes when the corresponding link is clicked. Such forum-membership features could eventually be integrated into the core functionality of a subsequent phpBB version, maybe by implementing actual groups.
BTW your signature recommends BlueHost, which happens to be hosting my svĀbhinava (website and associated) bulletin board since Dec. 04. My website had been on GoDaddy for 20 years, but Plex had no specific support for phpBB (actually the range of software offerings has dwindled over the recent years..). When I decided to implement phpBB and integrate it more tightly with our collaborative website, I followed the recommendation on your site and switched to BlueHost, which is indeed much cheaper and throws in https:// for free. I'm glad to have done so!
I also notice that you offer paid services which, at the moment, I need more for my website than for its phpBB section. Yesterday at noon (Chicago time), I ran a global search and replace on my local drive (within Expression Web) to replace Windows character encoding with charset=utf-8 (after the migration many legacy pages were not displaying special characters with diacritic marks properly). I then FTP'd all changed files (which included much more than those where the replacements were made...), amounting to over 7000. Since then, the website is showing directory listings instead of displaying the html (.php) pages as expected. My .htacess within public_html on the shared server is correctly configured.
BlueHost tech support says they can help only with their 'native' apps (e.g., WordPress) and not with custom code. And I am at a loss to figure out which other configuration-related files may have been overwritten (under public_html). But I suppose this would be easy for someone like you:
I've been maintaining our international collaborative publishing site as a labor of love for the last 20 years without paid subscriptions or donations. Instead, I often translate, edit, reformat, etc. the writings of others for free. But I'd be happy pay a reasonable fee out of my own pocket.
PS. Yes, I should have PM'd the 2nd part of my post. But I thought it might provide better background for my technical issues with phpBB...