The answer is yes, but allow me to rephrase your stated question, "Can the stock exhaust be modified?", to read, "How can I modify my stock exhaust?", since this seems, based on your following post, to be your intent.
The procedure was covered, extensively, in the early days of the Forum (use the "Search" function) and involves the application of two Bi-Metal Hole-Saws, an 1-1/4" and an 1-1/2", and two 12-inch Extensions, all available at your local Home Depot. You'll also need a powered hand-drill; 1/2" model works best, but a 3/8" will suffice. The entire apparatus is used to line-bore the muffler, top and bottom, end-to-end. The end result is very pleasing, acoustically, doesn't alter the structural integrity of the muffler, and doesn't require welding or re-painting; in fact, I'm still running with that set-up now, almost a year later. If you elect to go this route, I can offer you some further pointers. Hope this helps.