Here’s the list of names as set by default: http://hookr.io/functions/bbp_get_dynamic_roles/
You should be able to use:
$roles = bbp_get_dynamic_roles();
$print_r( $roles );
to see what the names of your roles are.
I’ve updated the filter code to make it work for BBPress 2.5.7+
https://gist.github.com/benklocek/433713bceb83eec6984f
The Keymaster title changed from “Key Master” to “Keymaster” at some point, and the filter only accepts 2 variables now.
I would be hesitant to use @robkk’s code, as it is replacing a core function, instead of simply filtering.
