This could be done on a regular basis. The mostly come in spray sheens. Avoid oil-based Moisturizers when in cornrows. The oils will only sit on the top of the hair leaving you with oily hair.
Instead use natural oil-based Moisturisers that prevent dryness and dandruff. Moisturisers with oils like olive oil and jojoba are the best. Use adequate amounts, focusing on the scalp to minimise itching.