If you’re curious, yes, you can upgrade your Vail Resorts passes (Summit to Colorado or Epic, Colorado to Epic). I confirmed that you can upgrade even after the pass purchase deadline.
I had opted for the lowest pass this season (Summit Pass: Arapahoe Basin, Keystone, Breckenridge) but had a change in plans (days at Beaver Creek). All I had to do was call the customer support line at 877-204-7881 and press ‘8’ to speak with a representative.
If you have your old pass (say you’re upgrading Summit to Colorado) and have previously owned a Colorado pass, you’re all set, they’ll simply re-activate the old pass.
If you don’t have your old pass, you can either opt to pick up your new pass at the office at Keystone, or they can mail the new pass (with additional shipping charges) to you directly.