You need to create whole image when developing a kernel, because of the separate FAT partition that does not support symbolic linking to your new kernel but when creating an image you can use symbolic linking. How to make an image, use the command
git clone -b some_branch some_armbian_repository
and study the image creation scripts in the lib directory. Armbian installer scripts do have some documentation too, but it is better to learn to edit the scripts for your liking.
After cloning balbes150 git, you can copy my edited lib files over the armbian lib files and create an image:
xfce@carrizo:~/Downloads/arm$ ./compile.sh BOARD=amlogic-s912 PROGRESS_DISPLAY=plain RELEASE=testing PROGRESS_LOG_TO_FILE=yes KERNEL_ONLY=no BUILD_DESKTOP=yes BRANCH=next CLEAN_LEVEL=debs NO_APT_CACHER=yes