Edit and modify existing pies

I need to know if we can modify existing pies.
Modify like remove a slice from one to another pie, replace a slice or delete slices.
What happens if we take out that slice?we still have that specific investment but as individually one? And what happens if we want to replace a slice,take out one and replace it with another.
If we delete one,that means we need to sell the stocks first to do so?

Thanks in advance :pray:t2: