I have a site where pages will often move from draft to published and then to legacy. I would like to create another status type similar to draft or published titled “legacy”. Wherein the page exists but is indicated as no longer active on the site.
Is anyone aware of a Plugin or way to hack this feature?
take a look at Edit Flow plugin which offers a suite of functionality to redefine your editorial workflow within WordPress. Features include Custom Statuses
You might try the Content Scheduler Plugin.
If not that one, then there are several from which to choose.
EDIT:
Since you don’t want an automated solution, then I would recommend just training your users to change the Post status to “Private”.