1st of all you can definitely target different areas of your chest. do 3-6 sets of a compound move for each section (incline,flat,decline) , and then 3-4 sets of an isolation move. The best single exercise for the development of the lower chest is DIPS. cross your legs behind you and lean forward, I always try to stay around 12 reps. Add weight with a belt if you have to. All I do for lower chest is dips, some other stuff you can try is decline barbell press, and decline dumbbell press. If you want to concentrate on the lower pecs do your dips 1st before everything else so your fresh and can hit them hardest.