Hey there!
As you guessed, the current way of adding custom kernel modules is to have a container build it at runtime and insmod the modules. We have an example repo that shows how to do that here
The problem is that we have multiple containers that require the modules, so I’m not sure I would want multiple containers having read/write access and attempting to install the modules.
As for this, I find it a bit confusing. If you follow the approach in the repo I linked above, once the custom module is inserted, it should be available to other containers with io.balena.features.kernel-modules and io.balena.features.firmware labels.
Let us know if this works for you or if you have other questions.
Thanks