Just curious, what do you believe using sas or rexx might accomplish? Fiddling with COBOL "copybooks" with either of these will only yield some generated code that references some copybooks. The output of which would still have to be compiled. There would be no "runtime" use of the copybook in the cobol code.
As has been mentioned, what you want to do is no task for a beginner and is a waste of personal and company resources.
I am working on a requirement where i need to pass the name of the copybook to a cobol program at run time.
Who in your management believes this is an appropriate "requirement" or is this just "something you wanted to look into"?
Possibly i misunderstand what your requirement actually is. From the earlier dialog, i may well not (understand).
You mention dynamically using the copybook - would there not be 2 - one for input and one for output?
As i mentioned, i believe i'm lost