Hi Nenad,
An another option which is not specific to django-admin-tools is to use django.contrib.staticfiles features: files in STATICFILES_DIRS take precedence over files found in app's static folders with the default config; both standard django admin and django-admin-tools are just an apps so you can override their static files by creating the same files (with the same paths) in your project's static folder.
E.g. if you want to override the base.css and your staticfiles folder is myproject/static, create the myproject/static/admin/css/base.css file and it will be used instead of standard admin's base.css. This works the same way as overriding templates (STATICFILES_DIRS == TEMPLATE_DIRS, STATICFILES_FINDERS == TEMPLATE_LOADERS).
You question seems to be unspecific for django-admin-tools. You may want to post such questions to
https://groups.google.com/forum/#!forum/django-users because django-users list has a larger audience and chances you'll get an answer for a general django question is better there.