Section 38K. In cities having a population of over one hundred thousand, the school committee may establish within the school department a bureau of public relations for the purpose of improving public relations between the school department and the community. Said bureau shall be under the control of a director, and such other assistants as the committee deems necessary may be employed to carry out the purpose of such bureau. The director and assistants appointed under the provisions of this section shall be exempt from the provisions of chapter thirty-one.