I do not think this is really a Mint-related issue, but I am really struggling to sort out a problem that may have a template solution!
How do I change the text that appears above the activity post box – the “What’s new in ?
My users keep posting lengthy topics here that are better-suited to group forums, so I want to add something at the end of the text that says “Please do not post full discussion topics here. Please use the Forums”.
So you mean the standard text for BuddyPress status updates in the activity stream?
These are in the BuddyPress template files provided with the theme. You could edit them there and/or add other explanatory text.
e.g. in activity\post-form.php
This is the form that appears in the main activity directory page.
Of course you will need to watch out for any changes when you update the theme, or I’m not sure whether a child theme’s replacement BuddyPress templates are picked up. If they were that would be the best place to put them.
The other way to edit the text in these files is to use a language file.