Do not put this in the FSX.cfg!!
This gets copied into the aircraft.cfg of the plane you are adding it to.
Drop the folder called 'texture.swair' into the 737-800 folder you are applying this paint to, then open the aircraft.cfg with note pad.
Inside you will see several sections similar to the one you listed here. Copy and paste this section below the last one you see and then change the [.XX] to the next number in sequence with the rest.
for example, if the last one is [fltsim.3], you would make this new paint [fltsim.4]. Any questions or problems, don't hesitate to ask.