Hi Ashok, I dont think it is possible to change the MyBasicMetadataAuthenticator internalClient password without incurring some restart downtime. Also to use the username:password, you can use it as auth details in your sql request header/ in the URL of your deployment directly.
URL Directly should be : https//{username}{password}@<Druid URL>
Request headers : Add the auth details (username,pass) as authentication param if using python