Well, firstly mate, I doubt that including the activation code to a program, on the actual CD / DVD would be very benificial to the Publishers, nor the creator, for obvious reason
I understand what you are asking, and agree it would be a good thing for the ' End User ' but it would be totally illegal to do it without the Authors permission, as it would be breaching any copyright that may be have been put in place by both the Author and the Publishers, insomuch as you would actually be changing the program Operational Code.
To do something like that you would need to have a very good knowledge of the basic programming principles and also in both Binary and Hexadecimal Coding, not to mention the more popular methods used, such as C++, etc. The best way to get to grips with programming principles is to start at the ' Grass Roots ' and practice making a simple program, and operating it, using good old ' Basic Programming Language ' as was used in the early DOS days
Basically a program is constructed of 3 parts, all of which are interactive with each other and certain criteria must be met to satisfy the requirements of each part, before it will pass on to the next.
The main basic parts of a program consist of ...
Argumentable
Conditional
Executable
Although not necessarilly in that order, the first two are the main factors that must be satifisfied before the executable will come into effect ... ie, the game / application runs.
Conditional sets out the criteria that must exist before anything further can be done .. this is where you will find the requirements for some form of activation to take place.
Argumentable does as it says, it gives commands of what should and what should not take place / exist, and gives arguement as to how it should be interpereted, when a particular action is carried out and what to do if criteria X-Y-Z are not met.
Executable will only come into play when both the Argumental and Conditional sections are happy with each other and they are happy that its needs have been met.
As said, this is only an absolute basic explanation, as different coding methods may use different terminology, but it might just show you that it is no easy task that you are thinking of.
Hope that has helped you a bit