Project 4.1 (yes, that old - sorry!)
Recently I had need to schedule work for one resource on a day set in the base calender as "non-working". I modified the day in question as "working" on the resource's calender but Project would not reflect the change in end date that the extra worked day should have made.

The problem was solved (albeit unsatisfactorily) by changing the base calender to show the time as working and then modifying all other resource's calenders to show the time as non-working again. A complete PITA.

Is there any way to have Project allow work on a non-working day on an exception basis rather than the method I was forced to use.

Grant Cartledge