Well, there are 2 questions in there :p
Usual boolean process :
- you selected both your primitives
- called the bool operation
- saw the result but no more primitives
>> if you just can't see any of the 2 primitives or meshes used for booleans (in your viewport it's normal, but I meant > even in the hypergraph or outliner <), check, as usual, if the "Construction History Button" is ON.
If you still can see the originals in the hypergraph or outliner, then you just can select any of the primitives and change attributes as described before, within the right pane "Channel Box / Layer Editor". Boolean will be affected too.
!!! as soon as you "delete history", both your primitives are thrown to bucket !!!
About definitely keeping original objects
now, select them both, go to Edit/Duplicate (option box), reset settings, apply. Put then the copies within (e.g.) another layer and even template them if they're kinda important basis.
Then, simply execute the boolean you want without anymore thinking about the primitives.
Hope that helps