I have a 2002 Grand Prix GT that has factory 5.25's in the doors as well as factory tweeters in the door. I am wanting to swap out the 5.25's with aftermarket but leave the tweeters the way they are. I am wondering how exactly the tweeters should be wired to the aftermarket. Should there be a high pass crossover on the positive lead heading to the tweeter?

I have no idea how the factory system is wired but if you put in a new tweeter, it will need some type of crossover to protect it.

The factory has the positive and negative leading out of the door to the factory 5.25. The tweeter has a clip on the end of the two leads coming from it that snap into a female clip on the side of the 5.25. I have heard there is some sort of crossover inside the factory 5.25 so I assumed after removing the factory 5.25 and splicing off of the wires out of the door that I would need to put a high pass crossover going to the tweeter.

that's probably a fair guess