It's not possible to make edits in UI as of now. In addition to @Ayub Khan 's answer , hive table can be altered using the hive command ALTER TABLE table1 SET TBLPROPERTIES ('comment' = 'your comments'); , and an update is sent to Atlas. You can see the updated comment in the UI.
For the second question , if hive table is created without any comments , it is marked "null". So it can be updated via REST APIs or through hive command itself.