custom record type fields

How do you add fields to a CustomRecordType?  From what I've read, you can only add fields on an update.  I've added the CustomRecordType and have the ID, so I tried to do an update, but nothing's working.  Here's what I'm currently trying:

         public void updateCustomRecordType()          {              CustomRecordType li = new CustomRecordType();              li.internalId = "22";              li.recordName = "License";              li.fieldList = createLicenseFields();                WriteResponse attempt = _service.update(li);                if (!attempt.status.isSuccess)              {                  string err = "Error(s):rnrn";                  foreach (StatusDetail sd in attempt.status.statusDetail)                  {                      err += sd.message + "rnrn";                  }                  MessageBox.Show(err);              }              else              {                  MessageBox.Show("It worked!");              }          }            public CustomRecordTypeFieldList createLicenseFields()          {              CustomRecordTypeFieldList fieldsList = new CustomRecordTypeFieldList();                CustomRecordCustomField liNumber = new CustomRecordCustomField();              liNumber.displayType = CustomizationDisplayType._normal;              liNumber.displayTypeSpecified = true;              liNumber.fieldType = CustomizationFieldType._freeFormText;              liNumber.fieldTypeSpecified = true;              liNumber.showInList = true;              liNumber.showInListSpecified = true;              liNumber.storeValue = true;              liNumber.storeValueSpecified = true;              liNumber.isMandatory = true;              liNumber.isMandatorySpecified = true;                fieldsList.customField = new CustomRecordCustomField[] { liNumber