Show a ManyToManyField as Checkboxes in Django Admin

From this answer it seems like it is possible to use ModelAdmin.formfield_overrides to override the ManyToManyField to use CheckBoxSelectMultiple:

from django.db import models
from django.contrib import admin
from django.forms import CheckboxSelectMultiple

class MyModelAdmin(admin.ModelAdmin):
    formfield_overrides = {
        models.ManyToManyField: {'widget': CheckboxSelectMultiple},
    }

I haven’t tried it and am merely quoting from the source, but it seems plausible. Good luck.

Warning: as @errx rightly pointed out, the documentation highlights the following caveat:

If you want to use a custom widget
with a relation field (i.e. ForeignKey
or ManyToManyField), make sure you
haven’t included that field’s name in
raw_id_fields or radio_fields.

formfield_overrides won’t let you
change the widget on relation fields
that have raw_id_fields or
radio_fields set. That’s because
raw_id_fields and radio_fields imply
custom widgets of their own.