I dug up the "stack" and found one good example of how to add new attribute to the field but it won't work.
$founderFieldset->addType('text', 'Amber_SupaSlid_Block_Adminhtml_Text'); $founderFieldset->addField('founder_name', 'text', array( 'label' => Mage::helper('vendors')->__('Founder Name'), 'required' => true, 'class' => 'required-entry', 'name' => 'founder_name', 'placeholder' => $this->__('Blah blah...') ));
in this case I got blank page (just navbar and title). In case I use:
$founderFieldset->addType('text', $fieldset->addType('text', Mage::getConfig()->getBlockClassName('supaslid/adminhtml_text')); );
Error 500 .... I forgot to mention that there is no errors in logs as well :) the only error I can see it console log where it deffinitely saying there is a code problem (500) so I assume the "renderer" does not work regardless it's position/location which is correct, class name as well.