For all: when swapping out either the blade or the HDD from a Fusion setup, you have to do a full backup to an external drive. Removing a drive will BREAK the Fusion drive like removing a drive in a RAID array.
After you upgrade, you have to re-create a fusion drive of the Blade and the spinner HDD. Google “do it yourself fusion drive” or search macsales.com (blog). After you build the new fusion drive, you can restore your backup to it (easy with CarbonCopyCloner, SuperDuper, etc.) You can even make a fusion of two SSDs.
If you are just changing the HDD, instead of removing the cable at the left, simply pivot the LCD 90 degrees counter-clockwise and gently set it back down. This allows one to access the HDD to swap.