Highlight text in the admin TinyMCE editor without altering the HTML source?

My own plugin stores a few short sentences from each article and I need to highlight them in the text editor so the author sees where they are and does not touch them.

The only way I found right now is using TinyMCE active editor’s search and replace function, wrapping the subject with a yellow span. I can then search and replace again and unwrap it.

    <script>

        jQuery( window ).load(function() {

            var content = tinymce.activeEditor.getContent();

                content = content.replace(
                    "the text to highlight",
                    "<span style='background: yellow;'>the text to highlight</span>"
                );

                tinymce.activeEditor.setContent(content);

        });

    </script>

Is there a better solution than undoing it on submit? How to handle if somebody alters the phrase and my unwrap function can’t find the spans?