At around 20-28 seconds, the video mentions tool’s center of gravity. This does not have anything to do with changing the GravityDirection of a release action. Center of gravity, in this case, is referring to tool’s center of gravity when picking objects. You could use a Define Tool Statement to reflect this parameter, and then use it for post-processing. However, for simulation purposes not physics, center of gravity is not used for picking and placing objects.
In VC 4.1, it is not possible to define tool’s center of gravity.
With tool definition you can set TCP (Tool Center Point) for the tool and nothing more. TCP is the used reference point when applying inverse kinematics. In the perspective of VC user, that is, the frame you move/jog around and snap to objects to teach the robot.
Center of gravity for a tool is usually used along with its weight data to compensate robot movements with this additional load i.e. to gain more accurate cycle times when simulating.
I hope this clarifies this topic a bit 
Yes, 4.1 does not support center of gravity. The tool frame defines the tool center point.
What you can do is add properties to the tool frame using API. For example, you could add a Real property to tool frame that allows you to define LoadMass, a Matrix or vector proeprty to define center of gravity. These, of course, are not used by the software. But the data is still there in the tool frame. You would just need to modify the post-processor to extract that data and map it accordingly.
Another option is to use a statement handler or python script to modify robot movement manually based on load and center of gravity properties that you add to tool frame being used. For example, if load is 10.0kg and center of gravity is 200mm along Z-axis, joint speed is reduced to go to next position. But remember, you have to do this all manually in 4.1.