createShaderOverride.py

from maya.app import renderSetup
import pprint
import maya.cmds as cmds


rs = renderSetup.model.renderSetup.instance()
ov = renderSetup.model.override
    
def addOverride(override_name, shader_name, node_names):
    
    render_layer = rs.createRenderLayer('l_{}'.format(override_name))
    collection = render_layer.createCollection('c_{}'.format(override_name))
    
    collection.getSelector().setStaticSelection(node_names)
    
    shader_override = collection.createOverride('so_{}'.format(override_name), renderSetup.model.typeIDs.shaderOverride)
    cmds.connectAttr('{}.outColor'.format(shader_name), '{}.attrValue'.format(shader_override.name()))
    

sel_list = cmds.ls(sl=True, long=True)
node_names = '\n'.join(sel_list)

addOverride('override_one', 'blinn1', node_names)
addOverride('override_two', 'lambert2', node_names)