By Default, the crafting mechanic will do as it did in Fallout 4.
- Check to see if the needed raw component is present in your inventory
- Check to see if a junk component that will yield the needed raw component is present in your inventory
- Same, in your stash
So to prevent a bulk being broken down, you need to have the raw material on hand.
But Bulking does not do what you think it does
But be aware. With only a few exceptions, Bulking materials saves you nothing at all. And I expect the exceptions come down to mistakes that will be corrected.
Take a look at this Reddit thread: PSA: "Scrap all junk" and then turn them into Bulk stacks in Tinker's Workshop before storing.
And more importantly, this one: With all the talk of "Bulk your stuff to save weight!" I made a simple spreadsheet to prove that it's not worth it.
With the exception of Lead and Aluminum, there is no savings to weight when Bulking up your materials.
Google Sheet: https://docs.google.com/spreadsheets/d/1WjWGNTadalTRvtG1MzzFqGVQ3YOWv5QgnurmNyudPZM/edit#gid=0
So why do it?
Bulking up materials is the only form of junk you can sell to a vendor. That's what it is designed for.
And it makes sense. Using some plastic to neatly wrap up your components, would not in any way make them weigh less.
The storage gain many see, after bulking up a tonne of materials (not including aluminium and lead, as noted above), is not from the bulking process itself. It's from the Plastic being consumed in the process of bulking.
A lot of misconception comes from people looking at in-game numbers, then doing math about the bulked version. What most are not aware of, is that the game does not list accurate weights. It rounds them to the nearest 1/100th. People also seem to get confused by the Pack Rat perk, which influences the numbers.
As an example, see: Weight miscalculations in stash box and inventory