Is it possible to manually switch off only one of the 4 USB ports of the BB XM?

Looking at the SRM at figure 40 there is a mosfet to allow to switch
off devices in what I assume is used mainly to stop devices that have
overcurrent. Is this right?

Is it possible to manually control these mosfets?, for instance I have
tried in /sys/..../usb/1-4/level /power but I completely failed. Do I
have to manually control the LAN9514 somehow to do this? We thought
that probably it is just easier to put our own mosftets after the USB
at 5V, but maybe if we can control those mosfets manually would be
awesome (and we would not need to put our own mosfets...)

I am not sure if this is supported in the driver or not. If it is, it should be possible but it would need to go through the driver. So check the driver and see what functions are provided. All of this is controlled through LAN9514.