I have a classmate who has registered and paid for the reunion, but would like to change his Attending Reunion status in his profile from Attending Yes to Attending Maybe. Neither the classmate nor I as the administrator appear to have the ability to make this change.
If this can be done "behind the scenes" the classmate's name is Tony Morefield.

It appears from his emails that this change is important to him.

Can anything be done?

Sorry, but there is no mechanism to set the Attending status to anything other than "Yes" for anyone who has completed a ticket order. The only alternative you have is to hide the Attending status icon on the Classmate Profiles page for ALL classmates.