Hi,
I regularly edit certain Gcode files, as the CAM program that generated it did not include an 'S' word (PCB-Gcode, a ULP of EAGLE PCB program), that requires four keystrokes per file, and three files per job, ie 12 keystrokes.....
no trouble. I use a Lua script (scripting language of Mach4) to edit a drill file generated by PCB-Gcode to get Mach4 compliant Gcode.

Both of these circumstances are very easy and can well be handled manually or automated with a script.

More advanced tool path editing requires Gcode be edited by hand, and depending on what alteration you want to make that can be tedious and/or error prone.

I use Fusion Basic, but I also buy a Machining Extensions subscription. Machining Extensions gives me simultaneous four and five axis, collision avoidance but also tool path editing, which is effectively
a visual edit of a tool path and that gets reflected in the Gcode. I seldom use it....but it is there. Typically tool path editing is available but only in the top tier PRO releases of PRO CAM.

Machining Extensions for instance cost me $2400NZD/year, and that is over and above Fusion Basic which cost $780NZD/year, so you certainly pay dearly for tool path editing.

Craig