Sun Jan 25, 2015 6:15 am
There's a button in the second set of special orders which allows you to change GHQ command. You can either 1) send your new commander to the same region, put him in the same stack, disable GHQ command, and reenable it with the new general, or 2) disable GHQ command for the current general and then give GHQ command to the new general regardless of where he is. Either way, you'll have to reassign your armies to the new GHQ.
On a personal note, I'd never change unless you use von Bulow (6-4-4) or manage to get von Mackensen promoted to 3 stars (5-3-2).