How to change the 'modification date' for an event?

We can allow a user to change the information they have provided. One of the options is to allow them to change it until a “modification date”. I cannot seem to find (in the options for managers of an event) any way to change this “modification date”. Was this an oversight, or is there a difficult-to-find (almost hidden?) way to configure this value?

Do you mean for registrations? Changing the registration form’s modification deadline is in the “Schedule” dialog. Also check the general settings of the registration form, there’s a setting until which point modifications are allowed (default is “never”, you probably want “until modification deadline”).

And in case this is about, after this weekend you will also be able to grant an individual registration an extended modification deadline.