Rules for modifying EXEC parameters

The following rules apply for modifying EXEC parameters:

You cannot modify a PGM parameter.
The calling EXEC statement can contain changes for more than one parameter and for the same parameter in more than one step in a called procedure. (If you code multiple overrides for any parameter in the same step, only the last specification will be effective.)
Modifying parameters should appear in the following order:
- Parameters without a procstepname qualifier.
- All parameters modifying the first step, then the second step, then the third step, and so forth.
You do not need to code the parameters for each step in the same order as they appear on the procedure EXEC statement.
You must code an entire overriding parameter even if you are changing only part of it.
You can use a different parameter to override the parameter in a procedure statement, if the two parameters are mutually exclusive. The override operation automatically nullifies the procedure parameter. This is an exception to the general rule that the only way to override a parameter is to specify it explicitly. For example, if the EXEC statement in a procedure contains a PARM= specification and you override it with a PARMDD= specification, the value specified by PARM= is nullified and the value specified by PARMDD= is substituted.