set ORM_segList [split $ORM_MSG r] ;# Create segment list using carriage return.
set ORM_PID_Seg [lindex [lregexp $ORM_segList {^PID}] 0] ;# Find PID segment.
set ORM_PID_fields [split $ORM_PID_Seg $Fld_Sep] ;# Split PID segment up into fields.
set newPid [lreplace $ORM_PID_fields 2 2 $ADT_mrn] ; # Replace old MRN with new one.
set newPid [join $newPid $Fld_Sep] ; # Put segments back together.
set ORM_segList [lreplace $ORM_segList 2 2 $newPid] ;# Group the segment list back together.
set new_ORM_Msg [join $ORM_segList r] ;# Put r carriage return back into msg.