Modifying procedures

There are two ways you can modify a procedure:

Using system symbols and JCL symbols
Using overrides.

Using system symbols and JCL symbols, you can design your procedures to be easily modified. If the procedure does not contain required system symbols and JCL symbols, you can override the statement.

For its current execution, you can override an in-stream or cataloged procedure by:

Overriding, nullifying, or adding EXEC statement parameters
Overriding, nullifying, or adding parameters to DD or OUTPUT JCL statements
Adding DD or OUTPUT JCL statements

Overriding a parameter modifies only that parameter; the system uses all other parameters on the original statement. For example, if you override the data set name on a DD statement that includes a UNIT and VOL=SER parameter, the system will still use the UNIT and VOL=SER parameters.

Invalid parameters in a procedure cannot be corrected through overrides. Before processing overrides, the system scans the original procedure statements for errors and issues error messages.