foreach $confLine (<$in>) {
	if ($confLine =~ /ip4-address address=\"/) {
		foreach (<DATA>) {
			my $ip = $_;
				if ($confLine =~ /ip4-address address=\"$ip/) {
				$confLine =~ s/\/>/update\"\/>/;
			}
		}
	}
	print $out $confLine;
}

___DATA___
1.2.3.4
1.2.3.5