This function takes a flex_prms_obj and sets certain values to the parameter matrix, based on the given instruction string (i.e., ' prm ~ conda => 0.3)
flex_specific_value(flex_prms_obj, formula_instr)an updated flex_prms object with a modified prms_matrix object, and (if applicable) a modified cust_prms matrix
flex_prms object
a string referring to "set" (see modify_flex_prms)