How much does it take to change the signature of a program or a dll? Can you simply add junk code and empty functions? Or do you need to scramble the variable names and function names? Or does the entire structure need to me rearranged?

As a computer science student I am interested in creating tf2/csgo/css and other VAC game cheats so I was wondering how much you need to change a program or dll after it has been detected to fool VAC.