How to attach units to a new HQ?

[Sixhits]

Greetings:

First post.

I'd like to learn how to attach full on sub units - platoons, for example - to a new HQ unit. I mean, moving C0, C1, C2, and C3 under B0, making B0, B1 (was C0), B2, B3, B4. Is this possible? From experimentation, I seem only able to attach units that are non-HQ units to other HQs - the C1s of the world.