Mass. Gen. Laws ch. 217 § 23A
In addition to the first assistant registers of probate provided for in section 23, the registers of the respective courts of the probate and family court department for the following counties may, with the approval of the chief justice of the probate and family court, appoint for terms of 3 years and may, with the approval of the chief justice, remove assistant registers with the same powers and duties. The appointments shall be as follows:
Barnstable, 1 assistant register
Berkshire, 1 assistant register
Bristol, 1 assistant register
Franklin, 1 assistant register
Hampden, 1 assistant register
Hampshire, 1 assistant register
Middlesex, 1 assistant register
Plymouth, 1 assistant register
Suffolk, 1 assistant register.
Those persons serving as assistant registers in the Barnstable, Bristol, Essex, Franklin, Hampden, Hampshire, Middlesex, Norfolk, Plymouth, Suffolk and Worcester divisions of the probate and family court department shall become assistant judicial case managers pursuant to section 23D in their respective court.
Mass. Gen. Laws ch. 217, § 23A