Hi Connaugh
I understand your situation with the stock is quite specific. Currently, the stock price of an item is averaged based on the prices of that item. If you want to remove the value for part of the stock and keep the prices for the rest, the app doesn't have a built-in option for that. A workaround is to create a new item as the equivalent of the old stock and use the build item feature to transfer the values from the old item to the new one.
Let us know if you need more help or if I misunderstood your question. And feel free to start a new thread if you need anything else.
Thanks,
Genreve