If the copyright year is always the current year, I wouldn’t save it in a blueprint. Rather put it in the template as a PHP echo.
Another idea would be to have a read-only field in the blueprint and update it with a page.update:after hook after changing the article. Keep in mind: If the page isn’t updated regularly, the copyright year might be outdated/wrong.
before property won’t work here I think. It is used to set an Optional text that will be shown before the input. It’s not actual input saved in a file I think. It’s like an usability help for the user to tell him what to type into the field.