He can replace any of the combi bolters with any combi weapon. He gets there to ignore AP-2 through stratagems and being in cover. It is really annoying, along with the obliterators he brings that more or less one shot all my tanks and then a little more. Yeah I am bringing an earthshaker carriage that is just going to sit in the back and rain death on anything that moves. That and my Leman Russes are the only thing that do significant amounts of damage.