#!/usr/bin/perl

use strict;
use warnings;

sub hex2str {
    my $hex = shift;
    my @bytes = unpack('C*', $hex);
    join(' ', map {sprintf('%02X',$_)} @bytes);
}

my $bin = qq{\x34\x65\xF5\x00\x55\x34\x65\xF5\x00\x55\x77\xED};

print hex2str($bin), "\n";

$bin =~ s/\x00\x55/\x22\xFF/g;

print hex2str($bin), "\n";