use strict;

open my $in, '<', "G203.xml" || die "Cannot open file: $!\n";
open my $out,'>' "_G203.xml" || die "Cannot open file: $!\n";

while (my $string1 = <$in>) {
  $string1 =~ s/XXXGASPOINTIDXXX/656563/gi;
  $string1 =~ s/XXXMMREFXXX/62394732472856563/gi;
  print $out $string1;
}

close $in;
close $out;