You need to reclassify the raster. To query by the original Grid value you can either use conditional statements in Raster Calculator or ArcPy or just look up the value in the CSV, of course.

In ArcMap you need Spatial Analyst Extension for this. If you do not have it and cannot afford it then you can try QGIS. If your reclassification is simple then use Reclassify. However, the fact that you have a CSV suggests that you might be better off with Reclass By Table. Your CSV forms the basis of your remap table.

You need to reclassify the raster. To query by the original Grid value you can either use conditional statements in Raster Calculator or ArcPy or just look up the value in the CSV, of course.

In ArcMap you need Spatial Analyst Extension for this. If you do not have it and cannot afford it then you can try QGIS. If your reclassification is simple then use Reclassify. However, the fact that you have a CSV suggests that you might be better off with Reclass By Table. Your CSV forms the basis of your remap table. The remap table is used as a look-up-table to create a second raster whose values will be the field value (in your case) that corresponds to the featureid in the original raster. In this instance, reclassification can be considered somewhat analogous to the results of a join.