This is not possible with ArcPy. To access this property, you need to use ArcObjects. You can do this from python via comtypes.
The following example is from mbabinski1988 on Geonet
First set up comtypes and snippets.py:
Accessing ArcObjects from Python?
ArcObjects + comtypes at 10.1 and newer
Then the following function can be used to return ...
The answers proposed are really time consuming. If you want to transform the symbology of several rasters, I strongly encourage you to try the following toolbox. It works like a charm!