Adding a Day Before Package Start Date

If I have 5 day tickets from a package that begin on April 21, is it possible to call and make them 6 day tickets but have them start on April 20?

I would call and ask. Do you have dining? If they say no, can you drop the tickets?

I do have dining. My plan was to call but I figured I would ask here first. I will post the answer after I speak to them!