Refer to figures.
In the southern hemisphere, frontal wind shifts are the mirror image of the northern hemisphere. 

Ahead of a warm front approaching South Africa, usually there is a north-easterly winds. After the warm front passes and the warmer air mass arrives, the wind shifts to a more north-westerly direction. It's an ANTI-CLOCKWISE rotation when viewed from above, which by definition is BACKING.

Back → CORRECT. In the southern hemisphere, warm front passage causes the wind to BACK (anti-clockwise shift). The wind shifts from north-easterly to north-westerly after frontal passage, which is an anti-clockwise rotation = backing. 

Veer → INCORRECT. Veering (clockwise shift) after warm front passage is the NORTHERN HEMISPHERE rule. In the southern hemisphere the rotation directions are reversed due to the opposite Coriolis force.

Remain constant in direction → INCORRECT. Frontal passage always produces a wind direction change as one air mass replaces another. The wind cannot remain unchanged across a frontal boundary.

Increase significantly in gustiness → INCORRECT. Significant gustiness is associated with cold fronts and convective cumulonimbus activity. Warm front passage brings stable stratiform conditions with steady, not gusty, winds.