Can you replace the exhaust on a 2004 Nissan Altima 25S 4 liter with one from a Altima SER?

If you could (and nothing is impossible) it would probably not be worth the trouble. First, the 2.5L engine is a 4-cylinder while the SE-R has a 6-cylinder engine. Their exhaust systems are completely different. Secondly, if you manage to adapt the new system to your car you will have to replace the rear bumper in order to accommodate the twin exhaust outlets. After all is said and done you would have gone through a lot of trouble and expense for very little, if any, benefit. Any performance gains will be offset by the extra weight of your new exhaust system. Consider instead a 2.5" exhaust with the appropriate header/muffler/resonator combination to achieve the performance/sound you are hoping for.