There is no functionality in the standard system for this. So the short answer is that it can not be done.
The long answer is that technically your partner could do it for your but most partners would not recommend it. It simply involves too many relations and dependencies to make it right.
I would adjust the inventory on the items so one of them goes to zero and add that inventory to the item i want to go forward with.
Existing sales orders or purchase orders needs to be updated accordingly. After that you block the item you don't want to go forward with.
