It would have to be the first cell in a pgc, with the splip flag set to false.
That or the start LBA of an actual file that wasn't in the middle of a vts set.
So basically you can't really change anything to make them excellent, they'll either be excellent or they'll be some rating below that.
If you had a first cell in a pgc with splip = true (if that's even allowed?), imgburn would set it to false anyway, so you'd go from 'very good' to 'excellent' with you having to do anything to it beforehand.