I tested the override flag and it worked for me.

#!/usr/bin/perl
use strict;
use warnings;
use CGI;
use Data::Dumper;


my $cgi = CGI->new;

print "Content-type: text/plain\n\n";

print $cgi->textfield(
            -name      => 'BillName',
            -value     => 'fake',
            -override  => 1, 
            -maxlength => 70,
            -size      => 50,
          );
[download]

If you want to preserve the user parameters in the HTML you don't need to specify -value => 'fake', as CGI will automatically fetch the value for the field.
When only one value is submitted these are synonymous:

print $cgi->textfield(
            -name      => 'BillName',
            -value     => $cgi->param('BillName'),
            -maxlength => 70,
            -size      => 50,
          );

print $cgi->textfield(
            -name      => 'BillName',
            -maxlength => 70,
            -size      => 50,
          );
[download]

However, if multiple values are sent for the same name, then CGI::param() will return the list of values, which has a similar effect as my previous post.