I am pretty sure you cannot make changes to amcas once it's already submitted and then just "resubmit". You would have to include extra info in the secondary or in an update letter.
After fall grades come out is a very common time to do this. Many would repeat the process in mid-spring semester to schools where they might be waitlisted or still waiting to hear anything.
Is it possible to update your GPA on AMCAS after you have submitted your application? I realize schools you have already applied to, you would need to update with them directly. But if you wanted to submit to more schools, which you can do after you have submitted, can you update your GPA? Or would you have to still update your GPA directly with those schools as well?