Basically what it comes down to as others have said above, don’t think that you can choose to binge on junk food and get off free. Being in ketosis or fat adapted is not a get out of jail free card to eat whatever once a week. There are things known as carb hangovers which can be as bad as a long night of drinking, dehydration, electrolyte wasting (keto flu causing), and various other problems individual people might run into.
However, if you’re hell bent on eating junk several times a month, you might consider incorporating a fasting regimen after the cheat times. The other part of this depends on your cheat meals themselves. Are you planning to pig out on extremely high carb meals? Or, are you talking about just introducing a few extra carbs?
If you find 20g of net carbs restricting and you are already at your goals, you could consider upping your carb allowance to 50g net carbs for example and see how you do on that. If that works well for a month with no ill effects, you might consider 60g even. Some people with healthy flexible metabolism and high energy expenditure through the day might even hit 100g safely. This advice may not apply if you come from being diabetic or highly insulin resistant.
If you don’t want to still restrict carbs and just want to have the cheat meals, keep them and possibly the meal after, extremely low fat. Which will hopefully mitigate the damage that high carbs and fat do together. Space out your other meals from the cheat meal itself. You could consider making it the last meal of the day and starting off high fat low or zero carb the next day.
Expect that eating high carb foods will cause cravings that can last for days and you may have that struggle.