Writing a Nanoha fic, and need to know something about the cartridge system

So for a certain scene I have in mind, I was wondering if it was possible for Nanoha to cast a spell (in this case, Divine Buster), then as she realizes it's not strong enough to pierce someone's defenses, she use a shell from the cartridge system to increase her energy output?

For example, like Goku using the Kaio-Ken x4 in his fight with Vegeta.

I feel like I only remember her using the shells before firing a spell, so not sure if she can do it while she's in the middle of casting it.