I don’t think its possible in Pega cloud. Essentially db access in cloud is kind of like a black box. You can use the Query Runner to normal SQLs, otherwise Connect-SQL can be used. But essentially you’re mostly relying on Pega GCS for most db actions.
I did explore further and as you mentioned we don’t have any OOTB way to run SQL and use connect-SQL rule to write the queries!
Reach out to Pega via a Cloud ticket, which Pega responded very quickly to run any DDL or query any information about the DB table or database. Even they help to run any query on our behalf.
Via activity we can use connect-SQL method to run DDL too, if needed.
So, we have options to update DDL but we can’t directly update/see DB table & schema details via tools like SQLDeveloper.
Hence marking this question as resolved as per this solution.