Assuming you have a numeric variable named DATETIME_VALUE that contains this date/time value, and you want to subtract two years, the INTNX command will do that. The format is irrelevant; if a variable contains date/time values, this works regardless of the format.
data want;
set have;
new_value = intnx('dtyear',datetime_value,-2,'s');
format new_value datetime24.3;
run;
--
Paige Miller