We'll need to figure out how we want to handle this stuff in the long run.  One thought would be a decorator so you could write code like

```python
@only.magstock
def check_shirt_matching(attendee):
    shirt_size_selected = attendee.shirt != NO_SHIRT
    shirt_color_selected = attendee.shirt_color != NO_SHIRT
         if shirt_size_selected != shirt_color_selected:
             return 'Shirt color/size not valid combination. Either set both or remove both'

def check_everything(attendee):
    check_shirt_sizes(attendee)
    ...
```

So basically we'd be able to define functions which do nothing unless you're running in a certain mode.  We could also have something like ``@all_except.magstock`` and whatnot.

For now, just putting if-statements seems like a sensible approach.