Perhaps some others in the #3dprinting community can shed some light on what's going on here.

I'm printing some name signs where the letters are raised by 0.8mm at the end. The base is PLA, and I'm changing to white PETG for the embossing.

I'd like the PLA to print at 215C and the PETG to print at 240C. (I already know it will all print at 215C)

I tried:

M600 R240

There was no temp change after filament swap.

1/3

@chrishuck isn’t it pretty well accepted not to try to print PLA and PETG together? Sorry for just questioning the premise instead of trying to troubleshoot the problem, but I’d do PLA on PLA for whatever this project is.
@chrishuck Chances are it won't stick anyway. I'd actually try to print both at 240° for that.
Can't help with gcode; I use m600 as it's implemented in my firmware and change temp by hand after that.