I don't think it's encrypted in the sense that you can just run it through a program and get the printout. (Look in functions.php and see if there's anything of interest there).
If this is decoded I'll contact the author of the theme and give him the money. I just don't want to buy his premium theme because I've changed all the files (styles/codes).
Interesting logic... Sometimes just contacting the theme author will quickly clear up a lot of questions about alternative theme licensing schemes and let you discover whether or not you can even purchase a copy of the theme without this "kill switch" gimmick built into it. You might also consider that depending on the source, your copy might have been modified in a manner not intended by the original author.
Those are pretty compelling reasons to contact the author and see if you can get a clean copy of the theme and a license directly from the source.