Adding a parm to a procedure/function

I have taken program CBX126 written by Carsten Flensburg (thank you,
Carsten - WAY cool program) and modified it for Journal Retention
purposes. In that program is a PrcCmds process with ExtPgm of QCAPCMD.
Then there is a procedure PrcCmd which receives a command string and
processes it with the PrcCmds process. (Please feel free to correct my
terminology - this is somewhat new to me...)
 
The PrcCmd procedure returns "-1" for an error. What I need is the
actual error code, in ONE use of this procedure. So...
 
I have changed the "PR" PrcCmd procedure to have TWO parameters, the
second one being:
 
    D  MSgIdRtn              7a    Options(*NOPASS)
 
I don't want to HAVE to pay any attention to the message ID except in
the one case where I need to know the specific message ID. I also don't
want to have to change the many other times this procedure is called.
 
I have changed the "PI" PrcCmd to include the second parameter, AND have
changed the ERRC0100 data structure to have all fields. That is, instead
of just having BytPro, I have BytPro, BytAvl, MsgId and MsgDta. 
 
Now when I debug my program, the %Error IF statement shows no error,
however ERRC0100 does show that there was an error, and MsgId contains
the message ID that I am looking for.
 
So, why does the CallP(e) not trigger the %Error any more? And second,
and probably more important, what is the "correct" way to accomplish
what I am trying to do?
 
TIA,

Dave 
612-371-1163