A recipe instructs to boil a whole head of cabbage, can I boil individual leaves instead?
The goal of the boiling step is to make it easy to remove the leaves. Removing whole individual cabbage leaves on a raw head of cabbage is tricky; they tend to tear.

If you want to put forth the effort, it should be just fine. They're cooked just long enough to soften them and make it possible to wrap them around the filling. I will happen much faster without a whole head of cabbage in there.