Is $id in the code snippet the parent/first post ID or is it the latest message post ID (won’t be parent ID if someone has replied)? What I’m looking to do is given a parent ID (the first message) make that message and all subsequent post ID’s read only.

add_filter( ‘fep_current_user_can’, function( $can, $cap, $id ){
if( ‘send_reply’ == $cap && 123 == $id )
return false;

return $can;
}, 10, 3);