Genosaurer wrote:
Depending on how corrupted you want them to be, you could always play them as a standard C:SM force.

 Seb wrote:
It should be noted that this is the fluff for the blood ravens in dawn of war 2 (or one of the extension, I can't remember). Basically, the librarian is possessed by a daemon and corrupts the entire chapter to rebel against the imperium.

 buddha wrote:
The fall to chaos is progressive and fairly inevitable once started, but that doesn't mean it always happens overnight.

Your force may be in it's beginning stages of damnation which means only its outlook has changed and functions otherwise as any chapter would.

If they are further down the line perhaps mutations have sprung up, insanity and violence more prevalent, and equipment looking decidedly less imperial as they scavenge more since they've been cut off from the munitorum.

If they've reached their apex then they will be indistinguishable from any other chaos forces. Perhaps they are fervent worshipers of one god (like the world eaters), the pantheon (iron warriors), or have no godly allegiance and wish only to sow terror and enhance their own power (night lords, red corsairs).

The cool thing is that your force can be represented at any time during their fall and the loyalist codex obviously represents them better in the beginning while the chaos dex best at their final fall.