I'm looking to alter the height of some cells within a raster and it's been suggested that I do this by creating a polygon layer and use that as a mask to alter only the heights of cells within the polygon.
The closest problem I've found similar to this is - How to change raster cell values within a polygon using QGIS GUI? - but I'm quite new to using GIS and don't understand how to do that though, I can't seem to control the extents of the polygon and can't find how to alter the heights.
Previously, I've tried using the Raster Calculator to create separate GeoTiff files in an attempt to alter the elevations and then merge the files back into a raster, I'm not certain if that sounds more straightforward, it just seems to give me an area with nan(not a number) rather than the elevations I want to input.
Another link that might be useful - Using polygons to apply unique value to all raster cells within those polygons?