Yes, you can change this e-mail address just like you can change any other user's e-mail address. NPrinting will not allow you to change it to an e-mail address that is already in use by a different user.
The Administrator is also a User. The Administrator can use the e-mail address to log into the NPrinting console (when authenticating with NPrinting credentials). Reports can be sent to that e-mail address when the Administrator is an e-mail recipient in a task.
HTH - Daniel.