$outdata = <<'__EOI__';
<cfmail to="#to_address#">
    ......
</cfmail>
__EOI__

$outdata =~ s{<cfmail}{<!--- <cfmail}g;
$outdata =~ s{</cfmail>}{</cfmail> --->}g;

print($outdata);

__END__
output
======
<!--- <cfmail to="#to_address#">
    ......
</cfmail> --->