@kellygoodmannp currently the inventory system treats variations like separate products. So if you put stock in different variations it adds them together for total stock.

You would be better off to set up a discount with the amount off that you are looking for for that item.  You could use a trick and use automatic discounts and set up a customer group for employees that automatically discounts them.  I think when you add them to the sale then that discount on those items would auto apply.  So you would have your regular 50% discount and then one for the items in 20% and you can specify in the discount tab in your online dashboard which items go to which discount.  This would automate the process for you.