The UBPorts image resides in the same main partition as Debian, so you don't need to delete either. The bootloader has extra boot options, and by using my script (attached) on your Cosmo alternative OS installer SD card thing you can flash the UBPorts boot.img to one of these boot options and essentially triple-boot Android, Debian and UBPorts.
You'll also need to put the boot.img on your SD card in the same folder and change its name to 'ubports-boot.img' for my script to work, and also add this:
echo "UBPorts,$MBF/Cosmo_Installer_UBPorts.sh" >> $INSTALLER_FILE
To the bottom of the list_installers.sh file (above the 'rm -f $PARTITION_FILE' line) and, as noted above, put the ubuntu.img file in the root directory of your Gemian install. Now boot to recovery with the SD card inserted and install UBPorts to another boot partition of your choice (But not the second one, as noted above there's no networking there!)
I've found the UBPorts image to be the most fleshed-out alternate OS yet - the camera works, keyboard layout works, 4G works, Bluetooth works 
Well I got a solid install of UB using the steps throughly, bu still ened up wiping Gemian I think. if you were genuinely able to boot Android, Rooted Droid, Debian and UB, I would lke to see it. the only thing I didn'y do is run that last line of code from step 1 in the top post. the only thing i didn't do was the last step of the first instruction post.
next flash the boot.img to one of the free boot slots using the following command "dd if=~/out/boot.img of=/dev/disk/by-partlabel/boot4 <- the last part will need to be changed to reflect you boot slot.
I was thinking about adding that line if code into the UBports-cosmo-installer.sh, loooking at the other installers I feel like that was the missing piece. buuuuut I am not code savvy enough to just through it in and hope for the best. also I think it needed edited a pinch to pull from the righ locations and the syntax seemed off.. I wish I could just image the whole device onto an extraneland the start from scratch , but I need another SD card for that. I'll let you know. WOuld love feedback on my theory.
AND ITS STUCK. Opening terminal, going through some sort of instruction/show of features and the screen won’t swipe to keeping moving through it.