Doubts related to parameters and arguments

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Hello everyone,
I had some doubts related to parameters and arguments

1) Are arguments associated with any namespace like ROS parameters are?
2) Is it that I can use my launch file arguments ONLY in launch files (directly, not asking through parameters)? Not in nodes and not even in xacro files or xacro macros?
3) Can I override the argument in launch file? e.g. Define an argument <arg name="robot_namespace" value="one"/> ---> Use it in one section of the launch file ---> then redefine it using <arg name="robot_namespace" value="two"/> ---> use it in second section of the launch file and so on
4) Can I override a parameter in my launch file instead of argument in 3)?