Fowler's, Working Effectively With Legacy Code. It'll teach you how to write maintainable code.
Don't go down this road. Do you want to be knee-deep in legacy code? Better go out and build your own stuff. Forget about the TAOCP, it really is overrated. Cormen is more recent and to the point. But don't read it cover to cover, but consult it when you need it. Furthermore, read the Dragon book (first one is enough) on compiler construction. Finally, learn to program in Standard ML, for example via the book by Larry Paulson (ML for the working programmer). That should be enough for the basic theory. If you got the above stuff under your belt, then this will take you pretty far. For the rest, rely on your mind and logic and feeling for elegance.