In order to manage .it domains using DomainRegister WHMCS module, you should add the following code to the /resources/domains/additionalfields.php file of your own WHMCS:

/* additional fields for .it domains
*/

$additionaldomainfields[".it"][] = array("Name" => "Legal Type", "LangVar" => "ittldlegaltype", "Type" => "dropdown","Options" => "1|Italian and foreign natural persons,2|Companies/one man companies,3|Freelance workers/professionals,4|Non-profit organizations,5|Public organizations,6|Other subjects,7|Non natural foreigners","Default" => "1|Italian and foreign natural persons", "Description" => "Legal type of registrant", "Required" => true); 

$additionaldomainfields[".it"][] = array("Name" => "Tax ID", "LangVar" => "ittldtaxid", "Type" => "text", "Size" => "20", "Default" => "", "Required" => true);

$additionaldomainfields[".it"][] = array("Name" => "Publish Personal Data", "LangVar" => "ittlddata", "Type" => "tickbox", "Description" => Lang::trans('ittldsez6'));

$additionaldomainfields[".it"][] = array("Name" => "Accept Section 3 of .IT registrar contract", "LangVar" => "ittldsec3", "Type" => "tickbox",  "Checked", "Description" => Lang::trans('ittldsez3'), "Required" => true, "Default" => "Checked" );

$additionaldomainfields[".it"][] = array("Name" => "Accept Section 5 of .IT registrar contract", "LangVar" => "ittldsec5", "Type" => "tickbox", "Description" => Lang::trans('ittldsez5'), "Required" => true, "Default" => "Checked" );

$additionaldomainfields[".it"][] = array("Name" => "Accept Section 6 of .IT registrar contract", "LangVar" => "ittldsec6", "Type" => "tickbox", "Description" => Lang::trans('ittldsez6'));

$additionaldomainfields[".it"][] = array("Name" => "Accept Section 7 of .IT registrar contract", "LangVar" => "ittldsec7", "Type" => "tickbox", "Description" => Lang::trans('ittldsez7'), "Required" => true, "Default" => "Checked" );

Third-level geographical .it domains

If you want to manage also third-level geographical .it domains. for every single extension you'll need to add a line of code like this, just afyter the previous:

$additionaldomainfields[".trieste.it"] = $additionaldomainfields[".it"];

.

edu.it domains

For .edu.it domains:

$additionaldomainfields[".edu.it"][] = array("Name" => "Legal Type", "LangVar" => "ittldlegaltype", "Type" => "dropdown","Options" => "2|istituto scolastico paritario,4|istituto scolastico paritario senza fini di lucro,5|istituto scolastico pubblico","Default" => "5|istituto scolastico pubblico", "Description" => "Legal type of registrant", "Required" => true); 

$additionaldomainfields[".edu.it"][] = array("Name" => "Tax ID", "LangVar" => "ittldtaxid", "Type" => "text", "Size" => "20", "Default" => "", "Required" => true);

$additionaldomainfields[".edu.it"][] = array("Name" => "codice meccanografico", "LangVar" => "ittldscode", "Type" => "text", "Size" => "15", "Default" => "", "Required" => true);

$additionaldomainfields[".edu.it"][] = array("Name" => "Publish Personal Data", "LangVar" => "ittlddata", "Type" => "tickbox");

$additionaldomainfields[".edu.it"][] = array("Name" => "Accept Section 3 of .IT registrar contract", "LangVar" => "ittldsec3", "Type" => "tickbox",  "Checked", "Description" => Lang::trans('ittldsez3'), "Required" => true, "Default" => "Checked" );

$additionaldomainfields[".edu.it"][] = array("Name" => "Accept Section 5 of .IT registrar contract", "LangVar" => "ittldsec5", "Type" => "tickbox", "Description" => Lang::trans('ittldsez5'), "Required" => true, "Default" => "Checked" );

$additionaldomainfields[".edu.it"][] = array("Name" => "Accept Section 6 of .IT registrar contract", "LangVar" => "ittldsec6", "Type" => "tickbox", "Description" => Lang::trans('ittldsez6'));

$additionaldomainfields[".edu.it"][] = array("Name" => "Accept Section 7 of .IT registrar contract", "LangVar" => "ittldsec7", "Type" => "tickbox", "Description" => Lang::trans('ittldsez7'), "Required" => true, "Default" => "Checked" );

Language variables

You'll need also to properly define language variables in your /lang/overrides/ directory.

For /lang/overrides/italian.php:

 #============================== domini .it ==============================

 $_LANG['ittldlegaltype'] = "tipo Registrante"; 

 $_LANG['ittldtaxid'] = "codice fiscale";

 $_LANG['ittlddata'] = "Publish Personal Data";

 $_LANG['ittldsec3'] = "Accett.ne sez. 3 contratto nic.it";

 $_LANG['ittldsec5'] = "Accett.ne sez. 5 contratto nic.it"; 

 $_LANG['ittldsec6'] = "Accett.ne sez. 6 contratto nic.it"; 

 $_LANG['ittldsec7'] = "Accett.ne sez. 7 contratto nic.it"; 

 $_LANG['ittldsez3'] = "(obbligatorio)";

 $_LANG['ittldsez5'] = "(obbligatorio)";

 $_LANG['ittldsez6'] = "(facoltativo per le persone fisiche, obbligatorio in tutti gli altri casi)";

 $_LANG['ittldsez7'] = "(obbligatorio)";

For /lang/overrides/english.php:

#============================== domini .it ============================== 

 $_LANG['ittldlegaltype'] = "Registrant type"; 

 $_LANG['ittldtaxid'] = "tax code (codice fiscale)";

 $_LANG['ittlddata'] = "Publish Personal Data";

 $_LANG['ittldsec3'] = "acceptance of section 3 of nic.it contract";

 $_LANG['ittldsec5'] = "acceptance of section 5 of nic.it contract"; 

 $_LANG['ittldsec6'] = "acceptance of section 6 of nic.it contract"; 

 $_LANG['ittldsec7'] = "acceptance of section 7 of nic.it contract"; 

 $_LANG['ittldsez3'] = "(mandatory)";

 $_LANG['ittldsez5'] = "(mandatory)";

 $_LANG['ittldsez6'] = "(not mandatory for natural persons, mandatory in any other case)";

 $_LANG['ittldsez7'] = "(mandatory)";