Since U-Boot is the boot loader you never need to flash to update kernel or modules. More on that further below.
One thing I would caution to double check on before putting too much effort into any kernel install is if you had correctly set the CONFIG_LOCALVERSION. To match the default kernels this tends to need to be set to “-tegra”. On your running install if you use the command “uname -r” this shows a version…the suffix of that is the CONFIG_LOCALVERSION. When a kernel searches for its modules it uses the “uname -r” to name a subdirectory of “/lib/modules/”…if not set correctly, then the modules won’t be found…or perhaps modules will be rejected if found and not compiled with the right CONFIG_LOCALVERSION.
If you started with a kernel config from “/proc/config.gz”, then you know your kernel you’ve just built is an exact match to the kernel which is running (provided you set CONFIG_LOCALVERSION)…thus you know any modules you’ve built are compatible with the running kernel. So assuming you’re new build only adds modules and does not change the base kernel the only thing you need to do is copy modules to the right part of “/lib/modules/
uname -r”. You’ll probably be able to figure out which subdirectory of that to place the modules in, but ask if you need.
So far as kernel install goes, look at file “/boot/extlinux/extlinux.conf”. There is a key/value pair “LINUX”, and the value names where the kernel is to be located…copy of a file here to that name installs the new base kernel. Don’t update the Image unless you’ve changed a base feature of the kernel (changs to something compiled directly in to the kernel and not as a module would need a new “uname -r”…a new CONFIG_LOCALVERSION…and then you have many more steps). For safety’s sake, if you have a serial console, then you can just add an alternate entry to extlinux.conf and keep the original boot entry. I also recommend never destroying the original Image or its support files…you can use extlinux.conf to use alternate names, e.g., you could copy the new Image to “/boot/Image-custom”.
So the question is if you’ve only added new modules, or if you had to change a feature of the kernel which is built in to it? Assuming it was just modules, then you just copy the module as noted above and perhaps run “sudo depmod -a” and you’re done. No flash.