I have not had any issues with adding a hop several times to reflect the different lots I have available. Just create a new hop, add in the new %AA and the amount and price and you are all set. Alternatively to 'add new hop', you can right click on the hops you want to duplicate and then paste it into the hop inventory. Edit it to change the important aspects (amount, %AA, price, lot no., etc.) and click save and you should be all set. If you just open the hop in your inventory and change the %AA it will change it for that entry and not add a duplicate entry.