I'd also like to shut off permissions to post to the forum in a 'social format' course, i.e. it would be just for announcements, not discussions - but where do I edit the roles and permissions for this forum?
Have you found the editing forum page for your social forum? Near the bottom of your social format course you should find an 'Older discussions' link which will take you to the view forum page then you can click the 'Update this forum' button. You can then change permissions via the override permissions tab.
Great, thanks for this Helen. I could indeed set the RSS and override permissions from the Updating Forum page, so all is now well.
For others' info, I did find, that the 'Older discussions' link was missing from the page, until there were 10 postings (can this setting be reduced anywhere?), but i was able to get to the Updating Forum page anyway with the URL: ...../moodle/mod/forum/view.php?f=1165&showall=1165 where 1165 is the forum ID.