That nut is the least of your worries.
To get the rear header pipe off involves quite a lot of strip down. The battery, battery box, plastic panel above the swingarm and the ABS unit needs disconnected. the 2nd nut can be removed easily then but getting the pipe out it a fair operation. I've done it but interfering with ABS module is a pain, it can be done without disconnecting it but getting the pipe out without damaging frame paint and bending battery-box plastics like some others have described on here to me is unacceptable. TBH, you should maybe consider leaving that pipe and doing the rest, it can barely be seen and as far as heat insulation, I don't think there is any to be had.
For heat insulation I wrapped that pipe around to under the heatshield at your knee. Even that was very difficult to do without stripping half the bike but it definitely does make a difference heat wise.