The main part of the rear pipe is 2 inches in diameter, with the larger part being 2.25 inches in diameter, so as long as the clamping part of the tip will fit over the 2.25 inch end, you can just slip it over that. Clamping it to the smaller 2.0 inch section should give a little security in case it vibrates loose, with the larger end section acting like a retainer.
If it's just a regular style angled chrome tip that is 2.25 inches in diameter on the inside, it might even just slide right over the stock pipe and give a semi-snug fit like that. Hopefully whatever tip you get is long enough so the clamp bolts go to the smaller section while the tip covers the stock pipe without having to cut anything.
Personally I'd advise against an exhaust tip, especially the chrome ones - they only serve as a place to attract rust, especially when put over other pipes, and the end of the exhaust pipe is a rust magnet on these Explorers already. They are also just a waste of money for something so blatantly cosmetic, and bolt-on tips are easily stolen.
If you want to clean up the exhaust pipe appearance-wise, I'd say use some high-temperature spray paint, either the flat-black paint they use for BBQ grills, or the paint made for exhaust manifolds/headers that comes in black or silver. You could even paint the small part of the pipe black, and the larger part silver, giving it the look of a custom exhaust.
If/when you feel up to getting a new exhaust, Dynomax makes a cat-back kit just for the 93-94 Explorer, with a Super Turbo muffler and a 2.25" rear pipe. I'd save the exhaust tip money for that.
