Assuming you are using PX4 v1.15 or earlier with the old rover module, then the MAVLink messages/values you can use in offboard mode are those documented here: Offboard Mode (Generic/All Frames) | PX4 Guide (main)
Those MAVLink messages map to particular uorb topics. The mapping isn’t documented but can be inferred from the names. You can also see what they might be in action by looking at the script you are pointing to. In other words, you can work out what topics to set from the mavlink messages, and see how that works in practice using the script.
@bradstaff Might be able to advise you if you can explain what you mean by “the script isn’t behaving as you would like”.