Modifying input fields
The correct method of modifying an input field is to create a new copy of it, and to change the address in the command-level parameter list to point to your new data.
Note: You must never modify an input field by altering the data
that is pointed to by the command-level parameter list. To do so would corrupt
storage belonging to the application program and would cause a failure when
the program attempted to reuse the field.