The global render settings are stored in the options node, which you can get with AiUniverseGetOptions(). If the universe isn’t active (you are not inside an AiBegin() / AiEnd() block so the scene doesn’t exist yet), AiUniverseGetOptions() returns None.

Once you have the options node, you can load options from an ASS file, or you can update it with the node parameter setters such as AiNodeSetInt(). The way kick, and pykick, work is that they load the ASS file first, with its options, and then update the options node with the values from the command line.

from arnold import *
import os

AiBegin()

AiMsgSetConsoleFlags(AI_LOG_ALL)

# Get the default options
options = AiUniverseGetOptions()

AiLoadPlugins( os.getenv( 'ARNOLD_PLUGIN_PATH' ) )

AiASSLoad("C:/Users/Support/project/scenes/test_640x480.ass", AI_NODE_ALL)

# Render using options loaded from the ASS file
AiRender()

# Change options and render with the changes
AiNodeSetInt(options, 'xres', 320)
AiRender()

# Load options and use them to render
AiASSLoad("C:/Users/Support/project/scenes/test_960x540.ass.gz", AI_NODE_OPTIONS)
AiRender()

AiEnd()