You have to edit the file /usr/local/.files . Open it with vi or nano and add there the path to usb_modeswitch.conf . Here is mine for example :
Don't forget to executeCode:# Enter full path of files to be saved via flashfs /etc/TZ /etc/fstab /etc/profile /etc/usb_modeswitch.conf
after thisCode:flashfs save && flashfs commit && flashfs enable && reboot