One of these fields is the ticket complexity. I've created the table "ticket_complexity" and associated it to the table "ticket". Then, I've created the file Kernel::System::Complexity.
On the CustomerTicketMessage.dtl I've added the following code (PS.: this field is a combobox, but I've created as a text field just to see if it would work):
...
<!-- dtl:block:TicketComplexity -->
<label for="Complexity" class="Mandatory">
<span class="Marker">*</span>
$Text{"Complexity"}:
</label>
<input title="Complexity" type="text" id="Complexity" name="Complexity" value="$QData{"Complexity"}" class="Validate_Required $QData{"ComplexityInvalid"}" />
<div id="SubjectError" class="TooltipErrorMessage" ><p>$Text{"This field is required."}</p></div>
<div id="ComplexityServerError" class="TooltipErrorMessage NoJavaScriptMessage$QData{"ComplexityInvalid"}" ><p>$Text{"This field is required."}</p></div>
<div class="Clear"></div>
</div>
<!-- dtl:block:TicketComplexity -->
...
Thank you.
--