"When you have recorded special prices and line discounts for sales and purchases, Dynamics NAV ensures that your profit on item trade is always optimal by automatically calculating the best price on sales and purchase documents and on job and item journal lines. The best price is the lowest permissible price with the highest permissible line discount on a given date. Dynamics NAV automatically calculates this when it inserts the unit price and the line discount percentage for items on new document and journal lines."Use this link to see more detail: Microsoft Docs NAV Special Sales Prices and DiscountsThere are Food and Beverage ISV solutions that have extended pricing functionality to deal with this and similar situations, there may be other horizontal solutions also available. You may want to consider one of these as an option over customization as they may also include other enhancements that you may find beneficial to your business. If you already have a food related ISV solution, you may want to reach out to your partner with this challenge, you may have a option available that you are not aware of.As for mass updating, @Lewis Rosenberg is correct, RapidStart is a greatly under utilized tool in NAV.Good luck!