Alright... rephrase for those who wish to make it difficult:
a program that allows you to slap YOUR ACTUAL OWNED AND MODIFIED car in it and see what it looks like with a spoiler or rims, simply by clicking two buttons isn't gonna happen..
unless you have a picture of your car at the exact angle, exact height, and exact distance as the referenced one... and then, it would only look marginal. Much more work to do all that than it would be to actually BUY rims and through them on there!

Ray