SUPERC is a tool. But if you are going to re-invent the wheel I and you do not know rexx then start reading the manual - Keywords, Functions and Parsing in particular. And then the TSO Extensions manual - EXECIO. And then the ISPF Library Services manual - most parts.
4. My suggestion is to VIEW the resulting OUTDD file after SUPERC finishes.
An alternate approach is to write a rexx program to VIEW a member of the production file and then have an initial editor macro that automatically issues the editor COMPARE command against the test file. The result is a panel that shows the differences in a member and where you can easily incorporate the differences.