I ran a test two years ago as outlined in this post. At that time, Easel g-code worked on Marlin. I’ve not run any recent tests. You must set up your job on your MPCNC in the specific way Easel expects. That is Z=0 is the top of the stock, and the XY origin of the job is the bottom left corner of the stock. If you are running your job from an SD card, you must rename the file to have a .gcode extension, not the default .nc extension.
Edit to add: If you want a footer as well as the header, the copy command looks like:
copy Header.txt+Out.nc+Footer.txt TheFile.gcode
And to reiterate, there are other scripting solutions. The CMD prompt is just available without installing anything.