weasley

The a/c button essentially enables or disables the chiller. In other words, if it is on, the climate control can blend heat from the engine with chilled air from the chiller to get the temperature desired. If it is off, the climate control can still blend hot air with ambient (outside) air to achieve a set temperature but obviously it can only get the cabin down to the outside temperature. At this time of year, that's not a problem but in the summer you will need the a/c on if you want the cabin cooled down.
Additionally, having the a/c on will assist with the clearing of condensation and mist from the windows, since chilling air also dries it.
The high/low auto setting essentially determines the force with which the fans will blow, which will effect how quickly the cabin reaches a set temperature. In the summer I tend to use the 'high' setting so that I can feel the cool air countering the greenhouse effect of sun through the windows.
The 'auto' setting will work with or without the a/c; it will control the fan setting, air direction and air temperature automatically.

I think this may be your best/quickest bet.  What I would add is that the panel is quite flexible and does take a bit of force to remove, so make sure you use a good, flexible, durable primer and paint.
 
According to partscat.com, the cover has two part numbers:
 
5L6807499  Cover  Rear
5L6807499 U34  aluminium silky smooth
 
Perhaps the former is unpainted?  Might be a better place to start?

Quite right... well spotted.So, my job involves a lot of technical training (I mean as a trainer). I state this as context to why I felt compelled to go out to my car, in my pyjamas, in the rain, to get these pictures by way of assistance. I can't help trying to explain stuff.
Anyway, looking at these pictures, the fuse you want is fuse 30, which in my fuse box is the yellow 20A fuse in the location eighth up from the bottom, on the right hand column (just above the green 30A fuse). In the lid of the fuse box there is a pair of tweezers for easy fuse removal. Note that your fuse box may have different fuses in it (either more or less... for example I have fuses in locations 14, 8, 3 and 2 which relate to towing, which you may not have). That said, fundamental ones (like number 30) should be common to all models.