Well this was not designed to remove the RSS button at all, this was to make it so if you go to,
external.php?type=rss,
external.php?type=rss1,
external.php?type=rss2 and the
external.php?type=html it will exclude the forums in the feeds.
Now of course if you go to a link directly, external.php?type=RSS2&forumids=39, it will of course show you the feed. Only way to not have it show is to not allow guests to see the forums contents.
It is kinda like having a forum, but you have it turned off. No one can see it, but if you know the link, you can go to it directly.
I can look into hiding the RSS buttons on the selected forums at some point. But I have another mod I am starting for someone so it may be a bit.