Modifying the price of an existing order.

I need to know if there is a way to change an existing order's price. Is there a way to take order 70 which is for $21.18 and apply a discount making the order $15.00?

Is there a way to have variable pricing where a "customer" can set their own price for an item?

I have a restaurant without a POS and would like to use this as my POS. I have everything up already. I just don't know how I can do a manager pricing type thing. For example if you want to buy 20 pizzas I can't charge the same as 1 or 2 pizzas. If we want to make a donation or just give a complimentary item to a customer. How can I do this?

One alternative I thought about was having a seperate hidden site for the store to use but I think that would get crazy after a while of all the coupon codes that could possibly be needed. I would think that there would be a price override setting somewhere in Zen-Cart already so that Admin could give a discount to a customer for an unforeseen circumstance.

Thanks for your input.

What do you mean by an 'existing order' ? If you can apply a discount to an order which has been completed, you can also apply a surcharge.

You can use attributes (or the Quantity Discount mod) to charge less for many pizzas than for one.

I am trying to use this as a Point of Sale in an actual store instead of buying one. So if you call the store to order a pizza we are placing a web order. Things happen from time to time and you want to give an unusual discount to someone for whatever reason. This is what I am looking to figure out how to do.

So by existing order I mean one that has already been completed on the checkout screen, emails have been sent.

Say I want to give you a complimentary dessert or 1/2 price dessert. Delivery driver forgot a soda and took it off the price. There are hundreds of possibilities of why you would want to override regular pricing. I am looking to get something to work on the backend(admin side). If I put discounts on the front end(user side) they are accessible to ordinary customers and again there would be dozens of discount codes. So my thinking is after the order is sent through from the front end to log in as admin and make the adjustment in price there.

There is the Edit Orders mod (link to v1.5 version). I haven't used it.

http://www.zen-cart.com/downloads.php?do=file&id=1513

would the Edit Orders module help you?
http://www.zen-cart.com/downloads.php?do=file&id=1200
You don't state which version of ZC you are using but I believe there is a EO 4.0 too for ZC 1.5

lol beaten past the tape again.

I am using version 1.50. I am going to install the edit orders module. I just read where it will allow you to edit the quantity of items but didn't see anything about pricing other than obviously if you had 3 items and take one off the price changes.
Unfortunately there are 60 some pages of posts for it so probably easier to install and try. I'll post back what happens. Thanks for the replies.

Thank you very much for pointing me to that mod. It does everything I was hoping for.

Thank you!!