Re: product attributes price modifiers affectec by other data
the processes performed when adding an item to the cart function start with includes/main_cart_actions.php at line 41, which calls the function actionAddProduct() in includes/classes/shopping_cart.php
You should note that adding a product to the cart doesn't necessarily fix the price: the price is recalculated when the cart is restored after logging in, when viewing the shopping cart page, and when proceediing to checkout. Those calculations are performed (eventually) by the function calculate() in includes/classes/shopping_cart.php
If you do decide to edit that file, be aware that it is a core file and there is no override capability for it.
Neville
An assumption is what you arrive at when you get tired of thinking...