Since you're here, we might want to create constants for the choices and default choices, ie
```
ACCESS = 'access'
...
CHARACTERIZATION = 'characterization'
NORMALIZATION_CHOICES_DISPLAY = (
    (ACCESS, 'Access'),
    ...
    (CHARACTERIZATION, 'Characterization)
)
```
And use the constants when we need to filter by command usage.  Should they go in the model that uses them, or in a common/constants file?  (or this could be a future improvement)