changing the heater matrix is very easy with the bottom of the dash out

there are 2 13mm nuts that hold the whole box in place and other than the 2 phillips screws that hold the cover in place in the engine bay, everything else just slides out of the way

very very easy swap, just undo the 2 screws that hold the adjuster rods in place, the 2 screws that hold the matrix in place and, with some luck, you can do the job in perhaps an hour