Here's a sample of how you might do it on a win32 box. It's very brute-force but does the job. It assumes that the file that you will be replacing all of the others with is named 'replacer_file.html' and resides in the same directory as the files to be replaced.

use strict;
use File::Copy;
use constant REPLACEMENT_FILE => 'replacer_file.html';
use constant DIRECTORY => 'C:/foo/';

opendir(FOO, DIRECTORY);
my @file_list = grep /\.html?$/, readdir FOO;
for my $file (@file_list) {
  unless ($file eq REPLACEMENT_FILE) {
    unlink(DIRECTORY . $file);  #remove original
    copy DIRECTORY . REPLACEMENT_FILE, DIRECTORY . $file; #make copy o
+f replacer & rename to original
  }
}
closedir FOO;
[download]

Hope this helps you along. One of the other monks may have a more elegant & idiomatic way of accomplishing this.