There is software available to edit raster data, but it is not exactly straight forward depending on the nature of the cleanup required. It can be easier to do if you can work with the classified point data and filter before generating a raster. This can be done in arcgis or qtmodeler for example.
However, in my experience with 2d urban modeling it is often easier to start with a bare earth DEM and add buildings with RAS using high n values in your landuse raster and good breaklines.