ST_SetSRIDdoesn’t change the coordinates but adds meta data to state what spatial reference system the coordinate actually are. If you stamped your WGS 84 long lat data as a meter based projection. Guess what? Its still long lat. A spade by any other name is still a spade so don’t use ST_SetSRID and expect to magically get meter coordinates.
ST_Transformis used to change the underlying coordinates from a known spatial reference system to another known spatial reference system.
In PostGIS 2+ it’s pretty easy to correct mistakes you’ve made with standard ALTER TABLE commands. We’ll demonstrate a couple of scenarios