Altering same table across multiple databases

Question

I have multiple databases on the same instance and I am in the process of updating a table schema that must propagate across all the databases.

I am not sure I know what the right procedure for this is but I think it should go a little something like this?

DO $$DECLARE r record;
BEGIN
  FOR r IN SELECT datname FROM pg_database WHERE datistemplate = false 
  LOOP
    EXECUTE 'ALTER TABLE public.' || quote_ident(r) || ' ALTER VARCHAR(200);';
    EXECUTE ...
  END LOOP;
END;
$$;

Any thoughts?