If you are going to use an exacto blade, be sure to use the back of the blade as a scribing tool, not the sharp cutting edge. Multiple light passes are best. I use a scribing tool myself, It gives a cleaner smaller cut that I prefer.
You will also need to add strip stock to the edges of the control after its removed. This is important inorder to achieve the proper scale gaps between the controls. The material removed would leave huge gaps that would look bad. Most flight controls have very little space between them on real acrft.. Don't forget to box in the spaces left after removing the control, especially when it comes to flaps. Hinges, brackets and actuators will most likely need to be built also.
Goodluck
Darren