Yes, you can appoint additional director as MD but the period of such MD will automatically end on coming AGM after his appointment unless you not regularize him.
11 October 2012
If a person while he was the additional director of a company had been appointed as the managing or whole-time director, the later appointment also ceases simultaneously with the cessation of his directorship at the commencement of the annual general meeting. However, if such a person is re-elected as full-fledged director at the annual general meeting and thereby he continues as a director of the company, he shall continue as a managing or whole-time director also for the period for which he is so elected by the annual general meeting.