there are options to flash.sh to reflash individually some (or every, I did not check) partitions, one by one, but is there an option to reflash everything behalve the rootfs partition.
And if not, is there a faster way than first extracting the rootfs partition and then reflashing it with all the other partitions ?
Yes, it is possible to reflash the kernel image and device tree without touching the file system. For that there is the option “-r”. So for example, if you want to replace the device tree you could use: