Sorry about the Buy Now button-code modifier checkbox; we have fixed that glitch now. We do make every effort to test everything thoroughly before we roll out any upgrade bugfix, but inevitably there are fringe cases we don't notice until someone brings them up. "Better" is the enemy of "Done", so eventually after testing everything we can think of, if we're to make any progress at all we have to roll out what we've got, as refined as we could make it, and then iron out any undiscovered wrinkles as they get reported.
We changed the location of Item-specific discounts to consolidate all discount settings in one common screen together, as the previous setup of having different discounts scattered in different places was just too confusing for too many sellers, and the previous placement of Item Discounts also led to other confusion and mishaps (e.g., sellers mistaking the Item Expiration setting for a discount expiration, mistaking the download attempts/hours settings for discount code uses/hours, etc.).
This also gave us an elegant solution to expand the functionality of Item-specific Discounts, so it's now possible to define those with a maximum use count and/or with minimum quantity/total thresholds, meeting the (very!) popular demand for product-based volume discounts. These new conditional settings for Item Discounts still will not work with Buy Now buttons (yet), but the previous functionality supporting a basic, unconditional flat discount off the unit-price will continue to work just as it always has for Buy Now buttons.
Unfortunately, we'd had no requests for discounts according to product category, and indeed we have no built-in way to categorize products (yet), so that would have to wait for a future release.
