Bro that DB is damn old, like 20 year old house kind..
But that doesn't mean old is not good.. just that maybe I don't think the old dB has enough MCB for your new use.

Don't need to talk to tnb ba as this is internal wiring and nothing to do with TNB meter outside as long as the wire from the tnb meter to the DB do not need to upsize.

But I am not electrician just my 2 cents