Is it permissible for a minor whose *tadbir* is valid to revoke it?

Primary text

If the validity of revocation by a competent person is affirmed, then the minor whose *tadbir* is valid may also revoke it. If the minor wishes to sell the *mudabbar*, his guardian (*wali*) acts in his place for the sale. If the guardian permits the minor to sell it, the sale is valid when executed by the minor.