Do not allow modifications after checkin

src/pretix/base/settings.py

@@ -1082,6 +1082,15 @@ DEFAULTS = {
             help_text=_('If your event series has more than 50 dates in the future, only the month or week calendar can be used.')
         ),
     },
+    'allow_modifications_after_checkin': {
+        'default': 'False',
+        'type': bool,
+        'form_class': forms.BooleanField,
+        'serializer_class': serializers.BooleanField,
+        'form_kwargs': dict(
+            label=_("Allow customers to modify their information after they checked in."),
+        )
+    },
     'last_order_modification_date': {
         'default': None,
         'type': RelativeDateWrapper,