Can we have a method to alter the costs as part of checkout?

I'd like it if there was some way where I could change the cost of each item instead of depending on the cost that's stored in the uc_store_credit_values table, much the same way that the price during checkout isn't the one in uc_products but is instead the price in uc_order_products.

Would people be interested in a patch that did that sort of thing?

---
In my case, I am selling attendance at an event, which costs a 'credit'. If the event is full, I don't want to charge a credit, I want to instead reduce the price to zero and put them on a waitlist. But there doesn't seem to be any elegant way to do this at the moment...