Yeah but that implies a lot of other things that no manager would be willing to do. Despite what Redknapp used to say, sending the lads out there to kick a ball isn't enough. You have a whole coaching set up with exercices designed to create patterns of play.
Changing your system basically means throwing away your little black book that you have patiently put together for your whole career. Of course, you can do that - in some cases, you should do that, for instance if you've spent a long time at the same club and you want to freshen things up but it's a lot of work and there's no guarantee you will get it right the first time around.
You'll make mistakes and you will gradually refine your training plan and your individual sessions. That's why people are usually willing to compromise (for instance, Mourinho giving more freedom to Aurier than he would to an ordinary right-back) but you won't find many people willing to get back to square one for twelve games.
These guys have a method and it works. It works because if it didn't, they wouldn't get these jobs in the first place. That's why Frank stuck to what he knew and that's why Tudor will probably stick to his system. He may fine-tune a few aspects to fit what he has available, but I really can't see him converting to a classic 4-2-3-1.