Modify containerd config without templating whole file

According to the docs, we can modify the containerd configuration by supplying a `config.toml.tmpl’ file. However, if I try, by using the bare template from here, containerd fails to start, complaining about the lack of a cni plugin configuration.

I could try to debug this, but it would be far simpler if I could just import an extra toml file with the extra value I want (I need to disable the GC plugin). Containerd supports this, natively, but k3s overwrites /var/lib/rancher/k3s/agent/etc/containerd/config.toml, on a restart, and removes the import.

Is there a way I can configure k3s to import a sub-config file for containerd?