Commissioner jurisdiction clarified: sole Commissioner or Board-empowered Commissioner to perform functions for an assessee. Substitution clarifies that the Commissioner competent to perform any function concerning an assessee is the sole Commissioner where only one has jurisdiction, and where multiple Commissioners have concurrent jurisdiction the Board shall empower the Commissioner to perform the function. Subject to that rule, for the purposes of Sections 253, 254, 256, 263 and 264 the competent Commissioner is the one who for the time being has jurisdiction over the assessee.