Well, if you're getting the complete package (spoiler, air dam, and hood) I would say, if you have time and are good at body work yes you could change it. In my experience, the rear spoiler itself is time consuming because you have to re-tape the spoiler every time you put it back on and then get the tape off the car every time you take it off(at least with my Bonneville, may be different for GP). The air damn is dependent on the fasteners used. Every time you change a hood you have to be careful of alignment with the other panels of the car. So basically it'* left up to what you're capable of or how much you are willing to pay for someone else to do it. Another thing is that you may also stress the paint the more you attach and un-attach the pieces, but that usually depends on how careful you are. But that'* all just what I would think.
2002 Pontiac Bonneville SSEI-XP
1974 Plymouth Satellite Sebring
1998 Dodge Ram 1500 Sport
1997 Chevy Camaro Z28 m6 5.3LS h/c/i/e