Inventor seems to have issues with modifying chamfers and filets. Restarting the program usually fixes it.
You can scale the design at anytime, but Inventor is designed to do everything in full scale size and scaling a huge drawing with complex shapes can take a long time.

@10 pups
Inventor 2015 HSM can do gcode, but regular Inventor does not do gcode. For that matter, most CAD packages do not do gcode without some kind of add on. If you want to learn gcode, I'd suggest looking at MasterCAM - it converts just about every CAD package out there into gcode for sending to a CNC. gcode really isn't all that hard to learn once you wrap your head around it.