I'm not trying to insult anyone but just pointing out a few things.
Most don't realize if you change planes in missions/campaigns you might change the whole dynamics of them.What if the plane you use doesn't have the same setup for bomb loads,external fuel tanks and so on? Maybe the performance of the planes is different. Missions/campaigns are setup for the planes that are used in them.You should take that into consideration before you start changing things.I understand everyone has their favorite when it comes to types of planes but you could mess up what the builder was trying to do.
TheBookie
I agree.
The best way to replace planes and ships is by manually editing the mission after, of course, having saved the original work elsewhere. I recommend Cody Coyote's mission building tutorials for correct manual editing.
Before doing that, make sure the Flight Models (*.air + aircraft.cfg) of the two planes are basically the same, to ensure the same performance of your replacement as the original, critical when it comes to AI behaviour. When I edit my missions, I usually replace only the aircraft I'll be flying, leaving the AI's untouched.
Likewise, the damage profile (*.dp) should have, if not the very same weapons, at the least the same loadouts, listed exactly in the same sequence as the aircraft called by the original mission. I routinely get rid of stock weapons, or otherwise ugly/oversized/etc. ones, replacing them with the best looking available.
If you don't want to go through weapon replacement, check out in Cody Coyote's tutorial how to change the code number in the mission file corresponding to the original loadout, in order to match it. Otherwise, you might end up watching your AI wingmates bombing the target with their droptanks, dropping bombs instead of firing rockets or doing absolutely nothing, compromising a good mission outcome.
Last but not least, as already pointed out by John, check framerate performance of your replacement against the one called for by the original mission author. A 'frame-hog' will impair your mission flow real bad!
Cheers!
KH 