Dynamic comments for product create/update form fields

You cannot set it from the database.
You will have to code for it.
You can make use of the after_element_html feature that the form builder offers.
So declaring a field like this:

$fieldset->addField('identifier_here', 'type_here', array( 'name' => 'name_here', 'label' => 'Label here', 'required' => true|false, 'after_element_html' => 'Some text after the element', ) ) 

will make your text Some text after the element appear after the element. It can be anything, even some html or javascript.
But there is a catch. The product add/edit form is not built using code as shown above. You cannot control each field. The fields are generated based on the attributes.
But you have the event adminhtml_catalog_product_edit_prepare_form that is dispatched for every tab that contains product attributes.
You can try to observe it like this (untested code):

public function prepareEditForm($observer) { $form = $observer->getEvent()->getForm(); //let's say you want to add some message for the attribute with code `donation` $donationElement = $form->getElement('donation'); if ($donationElement) { $message = ...determine the string to display.... $donationElement->setAfterElementHtml($message); } return $this; } 

There is also an other approach. Each attribute supports a custom form renderer. This feature basically allows you to have the input be rendered using your own class and your own phtml file. This seams like a more complicated approach, but if you want to give it a try check this answer. It's for a different problem, but the approach is the same.