#!/usr/bin/perl
$ModFile = $ARGV[0];
$Setting = $ARGV[1];

open (FH, "<", "$ModFile") or die ("Cannot open $ModFile.\n");
open FOUT, ">$Setting" or die "Cannot open $setting.\n";

$text = do {local $/; <FH>};

$text =~ s/^(Identity\s*\=)[^\n]*$/$1 ABC/si;

print FOUT $text;