Section 6A. No special judge of probate, register, assistant register or person employed in any registry of probate and insolvency shall be interested in, or benefited by, the fees or emoluments which may arise in any matter pending before the probate court or court of insolvency of his county; nor shall he act as counsel or attorney, either in or out of court, in any matter pending before said courts or in an appeal therefrom; nor shall he, except as otherwise provided, be appointed or act as executor, administrator, guardian, conservator, commissioner, appraiser or assignee of or upon an estate within the jurisdiction of his court; nor shall he be interested in the fees or emoluments arising from any of said trusts; provided, that nothing in this section shall prohibit the practice of law before said courts by a special judge of probate. Section seven of chapter one hundred and ninety-two and section seven of this chapter shall apply to a special judge of probate.