#!/usr/bin/perl -- 
use strict;
use warnings;
use Path::Tiny qw/ path /;
my $infile = '...';
my $outfile = '...';
my $find = VerifyHex( '\xe9' );
my $replace = VerifyHex( '\x65' );
my $IF = path( $infile )->openr_raw;
my $OF = path( $outfile )->openw_raw;
while( my $str = <$IF> ){
      $str =~ s{$find}{$replace}g;
      print $OF $str;
}
close $IF;
close $OF;
sub VerifyHex {
    my( $str ) = @_;
    if( $str =~ m/(\\[a-zA-Z0-9][a-zA-Z0-9])/ ){
        return "$1";
    }
    die "evil input $str";
}