i have seen engineers using a step down transformer for a step up transformer (33/11kv transformer primary side Star and the secondary Delta but now reversed in connections as 11/33kv)

1. what are the implications it?
2. if the practice is acceptable, what happen to the star point (neutral of the 33kv side)

 

No implications! A transformer is a bi-directional device.

 

However, there is a lurking gotcha: the insulation on the 33KV winding may not be sufficient for that voltage.