Hi @songiuno,
it’s possible using a filter. The plugin has several filters, that you can use for modifying something.

In our case, the filter hook is ubn_private_text_empty. This filter is executed when the text is empty, i.e. when the reader of a given page hasn’t any right to read that given paragraph.

For example, here is a function that can be added in the functions.php file of the current theme:

function image_when_private_content_is_empty( $text ) {
	$text = '<img src="' . get_stylesheet_directory_uri() . '/images/members.png" alt="" />';

	return $text;
}
add_filter( 'ubn_private_text_empty', 'image_when_private_content_is_empty' );

If the user cannot read the paragraph, the plugin will display the image members.png, as in this screenshot:

The line with gray background is the used shortcode, and the image is the result.

Hope everyone is doing well and staying healthy.

We are all fine, in this moment. I hope that you all are fine too. 🙂

You’re welcome!