We have a workflow in which a customer rents an item and is invoiced the correct amount when he returns it.  

Let's say we have a rental for a product for 10 days, and the item has a time based rule of 10 euro/day. When the customer picks up the item, he will know the pricing indication of 100 euro. The rental order is already confirmed now. 

8 days later, the customer returns the item. We can update the sales order line by updating the start and end times for the order, and the order line is adjusted to 8 days, and a 80 euro cost. 

Now here's the issue: 

Let's say that while the customer had the item, we changed the time based rule for the item to 20 euro/day. This customer should still only be charged 10 euro/day as that was the agreed upon price. When we adjust the order line to 8 days, it however updates the cost to the current time based rules, giving the customer a cost of 160 euro, while it should be 80. 

Does Odoo have a built-in workaround? 

With the current workflow, we would we need to create a new pricelist every time we perform a price adjustment, and that just doesn't seem manually manageable to me.

Ideally, Odoo would have some way of keeping track of the original time based pricing at the moment the order was confirmed, and use this for rental duration changes.