Change baud rate telem Pixracer

So according to the few informations here and there it seems that to change the baud rate of telemetry MAVlink I need to either change the init.d or make a extras.txt

First question is: why on the earth there is not a parameter to do that as in APM?
Second question: I can’t find the /etc folder on the SD, only the log forlder. Am I supposed to create both the etc folder and the extras.txt file? Where should I create the /etc (I’m on windows)? Do I need to use UNIX format?
Third question: I saw another topic where they use the following line of code in extras.txt to change the baud rate:

    mavlink stop-all
    set MAVLINK_F "-r 1000 -d /dev/ttyS1"
    mavlink start -d /dev/ttyS1 -b 19200 -r 1000

So what if I don’t want to stop all MAVlink but only telem1 for example?
What is the second line doing?
What is the -r param?
Why there is zero documentation about this?