CSS / Protected Content Filters | Really Useful Plugins

The following filter and snippet change the content protected options with additional styling and more branding to give you more control

<?php
function selective_custom_protected_content_output($output, $post_id, $purchase_link) {
    // Define an array of post IDs where the hook should apply
    $allowed_posts = array(362);
 
    // Get the post content
    $post_content = get_post_field('post_content', $post_id);
 
    // Check for the presence of the marker
    $marker = '<!--protected-->';
    if (strpos($post_content, $marker) !== false) {
        // Split content at the marker
        $preview_content = explode($marker, $post_content)[0];
    } else {
        // No marker, protect the entire content
        $preview_content = '';
    }
 
    // Check if the current post ID is in the allowed posts array
    if (in_array($post_id, $allowed_posts)) {
        // Generate the protected content output
        $protected_message = sprintf(
            '<div class="custom-protected-content-message" style="text-align: center; padding: 20px;">
                <p style="font-size: 24px; color: #007bff; font-weight: bold; margin-bottom: 20px;">
                    🔒 This content is protected.
                </p>
                <a href="%s" class="custom-purchase-link button"
                   style="background: #007bff; color: #fff; padding: 12px 24px; border-radius: 5px; text-decoration: none; font-size: 18px; display: inline-flex; align-items: center;">
                    <span class="dashicons dashicons-admin-network" style="margin-right: 8px;"></span> Unlock Access
                </a>
            </div>',
            esc_url($purchase_link)
        );
 
        // Return the preview content with the protected message
        return $preview_content . $protected_message;
    }
 
    // Return the original output if the post ID is not in the allowed array
    return $output;
}
add_filter('rup_sell_ind_posts_wsc_protected_content_output', 'selective_custom_protected_content_output', 10, 3);

The below snippet will protect all content and ignore the marker  and protect and style ALL content you could combine these two snippets for example to make one that ignores the marker on certain pages!

function custom_protected_content_output($output, $post_id, $purchase_link) {
    return sprintf(
        '<div class="custom-protected-content-message" style="text-align: center; padding: 20px;">
            <p style="font-size: 24px; color: #007bff; font-weight: bold; margin-bottom: 20px;">
                🔒 This content is protected.
            </p>
            <a href="%s" class="custom-purchase-link button"
               style="background: #007bff; color: #fff; padding: 12px 24px; border-radius: 5px; text-decoration: none; font-size: 18px; display: inline-flex; align-items: center;">
                <span class="dashicons dashicons-admin-network" style="margin-right: 8px;"></span> Unlock Access
            </a>
        </div>',
        esc_url($purchase_link)
    );
}
add_filter('rup_sell_ind_posts_wsc_protected_content_output', 'custom_protected_content_output', 10, 3);