You could do a slight introduction, maybe a week tops if you'd like. There probably isn't a ton of change that occurs other than a bit at the cellular level.
I am not an expert on this by any means, but I'll offer some input haha..
When switching back, I would stick to starchy stuff.. So not the cookies and brownies and breads and what not.. but more so the whole food approach of potatoes, rice, beans, whole grains, etc. Your energy might wain a little bit so maybe that is why you would want to do a slight introduction to get your body used to the more starchy carbs and whatever you may eat, so you aren't totally lethargic feeling. Because man, after fat adapted training... carb training is tough for me.
It doesn't sound like you are switching back to "pizza, soda, candy, etc." so I'm sure you will be fine!