For stb with the latest recovery on board (eg: Sf8008 - GbTri4k)it is possible to create further Multiboot slots (2-4-6-8-10-12-14-16-18-20-22-24-26) by connecting an external MicroSd or PenDrive (Octagon sf8008m usb2 port only).
On the created partitions it is possible to flash the chosen image.
For stb where it is NOT possible to install the latest recovery, the chosen image can only be installed on the 4 slots available on the flash.