The current guidelines regarding special counsels are contained in 28 CFR Section 600. CFR stands for Code of Federal Rules. The Code of Federal Rules is a list of rules established by the different agencies and departments of the federal government. The federal rules aren’t laws.
Power to appoint a special counsel is granted to the attorney general. If the attorney general is unable to perform their duty, the acting attorney general has the authority to appoint a special counsel.
A special counsel can be removed for misconduct, dereliction of duty, incapacity, conflict of interest, or other good cause, including violation of department policies.
Unless the special counsel is given permission by the attorney general or the acting attorney general, the scope of the investigation is limited to the crime(s) they were hired to investigate.