This compiles so I'm not sure what you mean by saying it won't compile
when you use value.
DATA_SECTION
number adjusted_pmax
PARAMETER_SECTION
init_bounded_number pmax(150,700)
init_bounded_number pmax_drift(-.2,.2)
objective_function_value f
PROCEDURE_SECTION
adjusted_pmax = value(pmax *(1+pmax_drift));
~