Apply format expression to X-axis label in SSRS Chart

I would like to apply conditional format to X-axis label. Currently mt x-axis label format is yyyy. Iwould like to apply M/dd/yyyy to my last label. When i try to apply below expression in custom format it print yyyy for all lable.

=iif(DateField=Variable!MaxDateField,"M/dd/yyyy","yyyy")

Is it possible to format the label or not in SSRS 2008r2?