Can I use the DPI interface and HDMI or TV out at the same time?
Nope! The DPI/HDMI/TV outputs are all the same hardware driver so you can only have one at a time. To enable/disable the DPI display, comment out or uncomment
in /boot/config.txt and reboot. It cannot be done on the 'fly'
How is that DTO blob made?
If you'd like to check out the device tree overlay and how to customize, you can read some more here: http://blog.reasonablycorrect.com/raw-dpi-raspberry-pi/
sudo apt-get install device-tree-compiler
sudo dtc -I dts -O dtb -o /boot/dt-blob.bin dt-blob-dpi.dts
to create your own!