Say i wanted to edit/manipulate a program

just wondering say i wanted to edit itunes, like change things about it etc not add ons plug ins actually edit the program itself

how would i do this

do you do this with software?

just intrugued at the moment, how i would do it

thanks if anyone knows

simple.

1. contact whoever wrote the program. (email, come over to his place, phone)
2. ask him kindly to send you the source code of the program.
3. when you have the source code, get proper IDE. for example Visual Studio.
4. open the IDE from the above step.
5. load the code in the IDE.
6. change the code.
7. compile the code with the IDE.
8. that's it, you have brand new program.

good luck!