You cannot do it to an arbitrary already running process using command-line arguments. The process has been started already and those arguments are already obtained and processed at this moment. It's too late to change its behavior.
However, you can design your process in some special way to implement something pretty similar. This process should communicate
with second instance of the same application, which would be a separate process. Using IPC, your second instance should communicate with the first instance and pass required data (say, taken from different command-line arguments you supplied on second run). Your first instance should listen to such connection and data and modify its behavior accordingly.
Actually, I designed a pretty elegant utility for such communications, which also can be used for implementation of single-process behavior of the application. I described it in my past answers:
Custom Windows right-click command launching multiple instances[
^],
Enter multiple commands to only one process instance[
^].
Actually, the author of the second question got to the same idea as yours; and I answered to that question.
—SA
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