I did a quick test using the Serial test app, where I can type in lines like:
#38400,7E1
And it reopens the serial port at the specified baud and format.  Note the formats the test app looks for is 7E1, 7O1, 8N1, 8N2.

Tested on an FTDI, PL2303 and CH341.  I also tested going to Teensy 3.2 CDCACM.  But as far as I know the teensy could not care less about Baud/Format.

Unless of course there is a way to query the value and use it to set a Hardware Serial port to it.

https://forum.pjrc.com/threads/45740-USB-Host-Mouse-Driver