Section 68. Chapter one hundred and fifty-three and sections two B and six C to six F, inclusive, of chapter two hundred and twenty-nine shall not apply to employees of an insured person or a self-insurer, nor to laborers, workmen or mechanics employed by the commonwealth or any county, city, town or district subject to sections sixty-nine to seventy-five, inclusive, who are entitled to the benefits provided by said sections, while this chapter is applicable thereto.