non-standard baud for Serial DAT ?

trying to control dynamixel servos directly via serial here - none of the servo’s baud rates are standard (1000000, 57142, etc.) Nothing similar available in Serial DAT pull-down. Tried entering baud rates manually, but they don’t stick.
Does baud need to be exact ? I’m having what seems like "out of phase " callback results, which I’m not sure makes sense. It could be my USBserial buffer isn’t clear and some bytes are hanging around? Is there a Python command to flush the USB serial ? Not sure if turning off the DAT achieves this…