There is no "side panel". Both sides and rear tail light are of one piece, from one side around to the other.
Yes, lots of things would be easier to deal with if that big body panel is removed (like replacing the coil, and rear shocks) - but as for the spark plug, yeah, takes a careful install. I place it in a locking spark plug socket which is attached to a short extension....and then thread if very carefully. I also remove the under seat bucket to do the plug replace....to get both hands in there to steady things....and more light.
The good news with an Iridium plug is that you'll only need to thread 2 or 3 in - in 100,000 miles. Specs I've read said they are good for 30>50,000 miles in a bike. I checked mine once after a few thousand to see the color - then spun a new one in (since I can't find spark-plug crush washers)....and forgot about it. If given no cause - I won't spin a new one in for a few years.
Stig