Overriding server-side validation rule from positive number to number in admin page

Question

I am trying to change a validation rule from positive number to any number (so it allows negative numbers too) for the following field:

[Admin Area] -> Promotions -> Catalogue Price Rules -> Add New Rule -> Actions -> Discount Amount

I have successfully changed the client-side validation rule but am struggling with the server-side validation rule.

Here's where I have got to:

app/code/core/Mage/Adminhtml/controllers/Promo/CatalogController.php

Mage_Adminhtml_Promo_CatalogController::saveAction

That function seems to fetch a rule_id from $_GET or $_POST and sends it to a load() method on the catalog/rule model, and then validateData() is called on that model with the data from $_POST.

I have searched all files for discount_amount but didn't seem to find any validation rules.

Answer 1

Found out how to do it.

app/code/core/Mage/Rule/Model/Abstract.php

Mage_Rule_Model_Abstract::_beforeSave

Override that file to the local folder and comment out the first bit of code in that method.