Distro-specific defaults can simply be put into the distro-calls. E.g.
```
class FreeBSDTimezone(ZonefileTimezone, Timezone):
    platform = 'FreeBSD'
    distribution = None
    default_mode = ZonefileTimezone.MODE_LINK
```
and here use:
```
try:
   return self.default_mode
except AttributeError:
  ... remaining code
```
```