Now I am wondering about the following:

Can I change the baudrate, databits, stopbits, and parity on the fly, that is without closing down the port and recreating it? I have my comm port handling routines in a thread and I am wondering what would happen if I kept the thread going, port opened, and just called SetCommState()?

Anyways, I am going to try...on my laptop...where the system limits seem to be the weakest.

Clearly, changing the comm port from COM1 to COM2 or anything else like that is changing the physical device, so that one can't do on the fly.