A user-replaceable program is a CICS-supplied program that is always invoked at a particular point in CICS® processing, as if it were part of the CICS code. You can modify the supplied program by including your own logic, or replace it with a version that you write yourself.
There are some general considerations that you must bear in mind when creating your own versions of user-replaceable programs:
For information about translation modes, refer to the IBM® ESA/370 Principles of Operation manual.