First, thanx for the DD"Swap out of it?" I hear you say. Yes, you can change your Doctrine path if you want. This will come at a cost. There will be a period of disorganisation for your army based on how far into your previous path you were and on the size of your army, so it's likely not something you want to do when things are going very poorly in the middle of a war. However, you do not necessarily start from scratch in your new Doctrine path: Several techs are shared between the paths, and if you switch to a path which includes a shared tech you have already researched you will start at that point in the new tree.
I imagine you mean that if your forces are heavily engaged, its a baaaad idea to switch Doctrine ? (rather than "going poorly" i mean). If so, Germany cannot switch really, except for the (historically) relatively calm period of post France, pre Russia (only Yugo and Greece in that period). Thats not trying to say that they'd want to switch of course, just thinking of if at any point old Iosef gives Adolf a solid right, and Germany ends up on the defensive on the Eastern Front, a defensive posture through Doctrine as such is pretty much out of the question ?
Or did you mean "disorganization" as a simple "you are X into tree A, and want to move to tree B, that'll cost each unit 50 organization points" type of thing, which might slow things down a bit if things go well, but isnt very dangerous, but would be an absolute disaster in a defensive scenario ?