#!/usr/local/bin/perl -w
use strict;

my $pagecode;
{
  local $/;
  $pagecode = <DATA>;
}

my $content = "Roger";

print "before:\n---------\n$pagecode\n";

# fix 1
$pagecode =~ s/<!--BeginContent-->(?:.|\n)*<!--EndContent-->/<!--BeginContent-->$content<!--EndContent-->/;

# fix 2
$pagecode =~ s/<!--BeginPages-->.*<!--EndPages-->/<!--BeginPages--><!--EndPages-->/s;

print "after:\n---------\n$pagecode\n";

__DATA__
<!--BeginContent-->Hello World!
This is a comment line
<!--EndContent-->
<!--BeginPages-->Hello World!
<!--EndPages-->