You could add to the Machine Configuration menu (Default, Haas Mill, Horizontal Mill, etc.) a machine like Simple G-Code that just ignores any unrecognized codes.
I sometimes use your program to check a path for a wire EDM program (Older Mitsubishi machines). EDM programs have some strange codes for power settings and stuff that I have to delete or comment out to get the path to display.
This line for example.
The EHH72 sets the power level word E, the H is just like # in Fanuc macros.
The FHH73 is the target feed rate.
And the HH74 sets the wire radius compensation, there is no word letter for this just that the variable accessed be in a set range (1 to 30) I think.
And this line.
The A word sets the wire angle to the value in variable 75, the problem here being the H again.
G02 X0.0000 Y1.5020 I0.0300 J0.0000 AH75
And instead of an O word they use the letter L for the program number.
Overall it is not a big problem. I have learned to do my text copy using the CTRL key to skip the problem lines so I just have to delete the AH75 word on one line.