Maya: Set Attribute On Renderlayer

msaor.py

import pymel.core

drg = pymel.core.PyNode('defaultRenderGlobals')

# dict of attributes and values to set.
# needs to include node name as well.
# Note that time values are divided by the framerate, ei. 10 frame / 25 frame/sec = 0.4 sec
attrs = {'defaultRenderGlobals.startFrame': 0.4}

# iterate over the selected renderlayers.
# can select renderlayers through the outliner with "Display" > "DAG Objects Only"
for layer in pymel.core.ls(selection=True, type='renderLayer'):

    # setup the layer override
    for attr in attrs:
        pymel.core.editRenderLayerAdjustment(attr, layer=layer.name())

    # finding the layer override through the connections
    # and setting the attribute values
    if layer.adjustments.get(multiIndices=True):
        for count in layer.adjustments.get(multiIndices=True):
            if not layer.adjustments[count].plug.connections():
                continue

            if layer.adjustments[count].plug.connections()[0] == drg:
                layer_attr = layer.adjustments[count].plug.connections(plugs=True)[0]
                for attr in attrs:
                    if layer_attr == attr:
                        layer.adjustments[count].value.set(attrs[attr])