Question 1: Is there a way to change the values in the cost or trackby fields for inventory already entered?
Answer 1: No. For any values entered in cost, trackbys, and others (the fields on the right side of the Add screen) including Serial Number, Lot, Date Code, Pallet, Supplier Code, Ref #, and Customer, you will need to Remove the inventory quantity (using the current trackby values), then Add that quantity back in with the different values.
Note: All trackbys must match when adjusting an item's inventory. For example, if you're trying to set inventory to zero, and there's a Lot trackby, make sure you specify the Lot number the same as the existing inventory, so the correct inventory will be adjusted. If you specify the wrong Lot number, you will adjust that Lot number, not the existing one, and the quantity of the desired Lot will not change.
Question 2: Is there a way to change what trackbys are required for an existing item?
Answer 2: You will only be able to change trackbys on items with zero inventory. For items with non-zero quantities, you'll need to record the values, adjust or Remove the quantity to 0, change the trackby settings, then adjust or Add back to the original quantities.