As far as I know, there is no strikethrough control on fonts in Creo.
You could add a true type font to the FONT folder that all characters have the strikethrough. You would have the change the font of the notes needing strikethrough to this font. I would expect this is about the same amount of work as sketching a line through a not but a font change could be automated with a mapkey.
(edit: @Tmetcalf, please move this to the creo forum)