Not sure if this will help with your issue, but I figured out how to completely remove password protected posts from the feeds (if they are password protected, I don’t think they should ever be in the feed).
Paste this code in your theme’s functions.php:
function filter_private($content) {
if(is_feed()) {
for($i = 0; $i < count($content); $i++) {
if(strlen($content[$i]->post_password) > 0) {
array_splice($content, $i, 1);
}
}
}
return $content;
}
add_filter('the_posts', 'filter_private');