I might be wrong, but I'm sure I found rules somewhere for player characters to join or leave a horde as a half action. Can't find those rules anymore though. Am I delusional?

I've never seen anything like that, ever.

Thaddux said:

You are not delusional.

See pg 350 of the Black Crusade Core Rules, the section titled HORDE VERSUS HORDE COMBAT, for the rules regarding PCs joining with and fighting as part of a Horde.

Thanks.

Could have sworn there was more to it than that though. Never mind, maybe there will be something in one of the upcoming books.