Executive branch offices, agencies and instrumentalities of the Commonwealth government and their respective functions and duties shall be allocated by law among and within not more than fifteen principal departments so as to group them so far as practicable according to major purposes. Regulatory, quasi-judicial and temporary agencies need not be a part of a principal department. The functions and duties of the principal departments and of other agencies of the Commonwealth shall be provided by law. The legislature may reallocate offices, agencies and instrumentalities among the principal departments and may change their functions and duties. The governor may make changes in the allocation of offices, agencies and instrumentalities and in their functions and duties that are necessary for efficient administration. If these changes affect existing law, they shall be set forth in executive orders which shall be submitted to the legislature and shall become effective sixty days after submission, unless specifically modified or disapproved by a majority of the members of each house of the legislature.