1 - No, it does not overwrite GRBL parameters (unless told to do so, similar to Easel)
2 - Many do *
3 - Yes *
(* - depending on work flow, design suites etc the proper post processor need to be used)
I use the x controller and UGS exclusively with my Xcarve. I design in Rhino and create 3d Gcode in Meshcam. I remove any codes that UGS doesn’t support by editing in Notepad. There are a few M codes that my post processor throws into the mix.
So you have 3D gcode and it won’t work with UGS or you don’t know what to do with it? I have the classic version of 1.09 downloaded to my laptop. There are tabs at the top of the screen. You would want the file tab for running a program. When you click on that, it allows you to go to your computer and click on the file you want to run. Then you hit " send". Then it runs each line. Occasionally you have to delete some things. The % sign is one of them.
I have always had trouble creating a valid gcode for easel now plan I start to understand how I do, but I still to work a lot without being able to start work