Switch Categories on a Specific Date?

I don’t know if this can be accomplished with WP alone.

I would create two custom fields for your posts.

1. First custom field would hold the date you want make the switch
2. Second field would hold the category you want the post to switch to

(Assuming it’s not always the same post and not always the same category)

Then I would write a cron-job (that runs daily) to run a php script with a SQL statement to check your database and make the necessary updates.