I should have explained this a bit better on the merging...my
apologies. And yes, I have the code behind the actual worksheet.

Cells N3 and O3 are merged and have a data validation list where you
can select Annual or Monthly.

Cells N4 and O4 are merged and contain a data validation list which
changes to either show a list of years or a list of months. In the
data validation properties for this cell, I have the following formula:

=IF($N$3="Annual",DATE_RANGE_ANN,DATE_RANGE_MON)

So, all I'm really trying to do is get the date format to change in the
N4/O4 cell when the annual/monthly option in N3/O3 is changed.

Hope this makes sense and thanks for taking the time to try to help...