A super useful node in Arnold is the aiColorJitter node.
You can utilize this for example to create object id based texture randomization in shaders.

• Drag and drop your texture files in the Hypershade
• Create an aiSwitch node and connect the File nodes as inputs
• Create an aiColorJitter node
  Set the Type to Object
  Set the Input Color to black (0,0,0)
  Set the Gain Max to the number of inputs (max ID + 1) minus a little number (for example 6 – 0.001 = 5.999)
  Connect the Out Color R into the aiSwitch node as Index
• Connect the aiSwitch Out Color into the shader.

Done.

notes:

• You can use this method with MASH network generated instances of course
• Of course it works with OSL shaders as well (which using custom file name inputs).
  For example:
  File node/File Texture Name -> aiOSLShader/Filename (a custom input) -> aiOSLShader/Out Value -> aiSwitch/Input # -> aiSwitch/Out Color -> aiStandardShader/Emission Color
• The aiSwitch node can utilize 20 different inputs.

Cheers, D