I am sorry; you cannot load g-codes into the simulator. The simulator will only simulate the toolpath curves from Rhino. In most cases, you shouldn’t need to edit the g-codes. It is much easier to control the toolpath by using region curves and clipping planes. It shouldn’t be necessary, but It is also possible to edit the toolpath curves in Rhino. If you need to edit a toolpath in Rhino you must ungroup the toolpath curves before editing them. When the toolpath curves are ungrouped, they will no longer be recognized as toolpaths from madCAM. This is for safety reason because if editing the toolpath curve, madCAM need to recalculate the rapid traverses. After editing the curves, use along curves from the curve milling and select the ungrouped curves and madCAM will recalculate the rapid traverses and make a new toolpath group.
If you need help, please send the model to madCAM support and we will create some sample toollpaths for you.