You can add tag objects.

taggit/managers.py

@@ -105,6 +105,7 @@ class _TaggableManager(models.Manager):
     @require_instance_manager
     def add(self, *tags):
         for tag in tags:
+            if not isinstance(tag, Tag):
                 tag, _ = Tag.objects.get_or_create(name=tag)
             TaggedItem.objects.create(object_id=self.object_id, 
                 content_type=ContentType.objects.get_for_model(self.model), tag=tag)

taggit/tests/tests.py

@@ -34,6 +34,9 @@ class AddTagTestCase(BaseTaggingTest):
         apple.tags.remove('green')
         self.assert_tags_equal(apple.tags.all(), ['red'])
         self.assert_tags_equal(Food.tags.all(), ['green', 'red'])
+        tag = Tag.objects.create(name="delicious")
+        apple.tags.add(tag)
+        self.assert_tags_equal(apple.tags.all(), ["red", "delicious"])
 
 
 class LookupByTagTestCase(BaseTaggingTest):