Bug: Classified renderer allows the break values to be adjusted higher than the maximum value of the raster but not lower than the minimum value
When attempting to change the break values to apply to a greater range of values, the maximum value can be adjusted to a value larger than that contained in the raster; however, the minimum value can not be changed to a value lower than that contained in the raster.
This is a known issue with the Classified renderer.
Create a raster that contains the range of values needed.
Save it as a layer file.
Use the layer file to import the symbology to the desired raster.