5Where since the commencement of the three last pre-war trade years a trade or business has changed ownership, the provisions of this Part of this Schedule shall apply as if a new trade or business had been commenced on the change of ownership, except in cases when the taxpayer makes an application that the provisions of Part III of this Act and this Schedule should apply as if the trade or business had not changed ownership, but in that case such modifications (if any) shall be made in the application of this Schedule as may be necessary to. make the basis on which the profits standard is computed the same as that on which the profits of the accounting period are computed.