Yes, Disneyland Resort (California) allows you to "upgrade" a 1-day theme park ticket to a higher tier by paying the difference in price. This is a common necessity if you originally purchased a "low-demand" tier ticket (like Tier 1 or 2) but later wish to visit on a day that requires a higher tier (like Tier 5 or 6). To perform this upgrade, you must generally visit a Main Entrance Ticket Booth or contact Disney's Guest Services before the ticket expires. You cannot "downgrade" a ticket to receive a refund. Additionally, the amount paid for any wholly unused and expired ticket can be applied toward the purchase of a new ticket at the current market price, provided the new ticket cost is equal to or greater than the original amount paid. It is vital to remember that a ticket "upgrade" does not guarantee entry; you must still secure a valid park reservation for the new date, which can be difficult during peak seasons.