Sections 63-3035 and 63-3036, Idaho Code
If a business is sold, the new employer is to apply for a new withholding account number and file separate returns and W-2s. If a change in the form of doing business requires a new federal employer identification number, the new entity is to apply for a new withholding account number. Neither entity should report wages paid by the other entity, nor use the other entity's withholding account number.
Idaho Admin. Code r. 35.01.01.870