Upon the effective date of this section, no school service personnel shall be permitted to become employed in more than one regular full-day position, nor more than two one-half day positions at the same time: Provided, That nothing herein shall be construed to prohibit a school service personnel from holding an extracurricular assignment or assignments, as provided in section sixteen of this article, or summer positions, as provided in section thirty-nine, article five, chapter eighteen of this code, nor from performing extra-duty assignments, as provided in section eight-b of this article, in addition to his or her regular position.