If I get a D on Calculus AB and drop it for 2nd semester, I was planning on taking Calculus I for that 2nd semester instead at a community college instead of HS. Would that replace my GPA to a 4.0 instead of a 1.0 if I get an A on calculus I 2nd semester.
It depends on your school. Ask your GC.
I meant by replacing the score on your college application. 
Since I heard colleges tend to use a different mathematical formula than the GPA on your HS transcript.
It still depends on how your school reports it. It will probably be on your transcript, so colleges will probably see the bad grade.