[Django]-User with permission to modify only one field of the model in the Django Admin

Have a look at Django Guardian. That provides more flexibility in assigning permissions on various levels. Django only lets you set permissions at object level, so in your case you were only able to set permission to create/edit/delete Client objects.

http://django-guardian.readthedocs.io/en/v1.4.8/index.html

If that doesn’t suffice, there are a few other packages with the desired functionality:

https://djangopackages.org/grids/g/perms/