Modifying an existing subfile RPG 3 program

HI Guys,

  I have here an older RPG program to modify. I say RPG 3, bec. it is
using 'E' specs amongst others.

  The program displays data in several forms. One is the Subfile list of
header records, w/ a FOLD that then displays individual records, perhaps
as a subfile also ( a screen of the entire record detail), and in other
non subfile ways. There is an exisiting provision for changing some data
but I have not seen this work. (Apparently not all of the features work
perfectly).

  I need to add some additional functionality. To allow users to modify data.

Since this is a subfile that will have to be updated as well. I am not
sure if it is better, to add a change code on the listed subfile data of
the header records, or to put the change in, on the detail display.

My concern is that I will be tampering w/ the RRN or perhaps other
processes the programmer put in, if I mess around w. the subfile too much.

Perhaps one of my good friends on this list can comment.

Thanks,
Steve