while (my $line = <$rfh>)
{
  if($line=~/^\s*([^=\s#][^=#]+?)\s*=/)
  {
    my $key=lc($1);
    $line =~ s/(=\s*)[^#\s]+/$1$changes{$key}/ if(defined($changes{$key}));
  }
  print $tfh $line;
}