Hi Shelley,
I think you're on the right track! Have you explored the Dynamic Shipping method system table table before? It's called LTR_TNEW_DYN_SHIPPING_METHOD and allows you to add a row, just for that event and default it to "Hold at Box Office." But then you can also use the Alias field to rename it something like "check in at door."
Hope that is helpful,Karyn
P.S. With all system table changes, make sure to hit save and clear your admin cache to see it display immediately on TNEW.