By "partially remove" is this heater case connected/ clipped together in the midddle?
You may be able to disassemble the left half of the box/ remove the heter half with the core, without taking the box completely out....
If it is seamed top to bottom (it will be held together with spring clips, screws, or a combination of both).... that may be a possibility. If it is seamed horizontally, you most likely have to take it completely out to disassemble it.
Hard to tell from Alldata, but they are saying to remove it completely (which means evacuate the A/C system as well... but, that may not what you HAVE to do. Mk. 2 heater cases said you had to, but I have done those in the car, just removed the center console.