We're not 100% sure if this will answer your question but the system management jobs run based off of schedules and those schedules should have parameters. So if you hit /api/v2/schedules you should see schedules there for your system jobs and those should have extra data. For example, my cleanup activity steam has extra_data of:
So you could change the parameters to the schedules outside of the GUI using whatever tool you wanted.
Let us know if this is what you were looking to do.
-The AWX Team