How can I add the words (registered users only) next to quick reply.
see below:
hmm, im not sure u can do that, or maybe u can try looking in ur board settings.
Edit showthread.lang.php
It is located here:
/YourForumDir/inc/languages/english/showthread.lang.php
Find
$l['quick_reply'] = "Quick Reply";
Replace with
$l['quick_reply'] = "Quick Reply (registered users only)";