Multiple Conditions for Custom Codes ("OR" and "AND")

For encouraging a guest to extend their stay, I have to create two separate custom codes. One for if the night after their booking is open, and one for if the night before their booking is open. I would like to be able to send a message if the night after OR the night before is open, and include the pricing of what that night would be if they added it with a custom discount (eg 25%). Otherwise, I have to have wording in each custom code that would sound okay even if the other code does not get triggered, which is clunky.