Cool [Q] Building Android 4.4.x custom upgrade

Hi experts,

I'm new to building Android ROM. So please correct me if anything doesn't make sense

I have a device that's currently running Android 4.2.2 (Amlogic 8726-mx). I have all necessary source code including uboot, kernel, 4.2.2 source.

I have two questions
  1. Can I use the existing kernel, uboot source code and merge with the Android 4.4.x source code from google?
  2. If yes, is it just simply replacing the "system" folder and then run make command to build? If not, can anyone point me to the right direction?

Thank you all in advanced