Checkout the new rules and missions for the Horus Heresy Betrayal at Calth that are included in the inaugural issues of new monthly White Dwarf.
Reinforcements have arrived for the Ultramarines in the underworld wars, plus way to play the betrayal at calth by swapping units as well.
Source: Scanner
Overall I like the update and alternate rules for the game, which gives hobbyists new ways to play this venerable game.
Checkout out the rest of the new rules Betrayal at Calth below: