My words literally betray me.
I have 2 bomb cards in front of me. I take one die for one of the cards, but the other die doesn't work for the second card. The first dice taken completes that bomb card. Can I take that card away and replace it with a new card and then use the leftover die on the new bomb card instead of treating it as an unused die?
Nope. You place all dice. Then you get new cards.