Creating a custom template, based on some existing LXC template after running the instance at least once

(Please note that [this question](https://unix.stackexchange.com/q/258164/5462) is about LXC 1.x, whereas *this one* is about LXC 2.x/LXD) I scoured the web for an answer to this one, but couldn't come up with any reasonably non-hacky answer. What I am looking for is an approach to fashion an existing template a way I'd like to. In particular what I'm after is to customize the upstream Ubuntu cloud image by making various changes in its root FS and adding/changing configuration. So my current approach is to lxc launch ubuntu:lts CONTAINER and then use lxc exec CONTAINER -- ... to run a script I authored (after pushing it into the container) to perform my customizations. What I get using this approach is a reasonably customized container. Alas, there's a catch. The container at this point has been primed by cloud-init and it's a container instance, not an image/template. So this is where I'm at a loss now. What I would need is to turn my container back into an image (should be doable by using lxc publish) and either undo the changes done to it by cloud-init or at least "cock" cloud-init again so it triggers the next time the image is used as source for lxc init or lxc launch. Alternatively, maybe there's a way to completely disable cloud-init when I lxc launch from the upstream image? Is there an authoritative way? Even though I looked through all kinds of documentation, including the [Markdown documentation in the LXD repository](https://github.com/lxc/lxd/tree/master/doc) as well as the blog series by Stéphane Graber (LXD project lead), [especially \[5/12\]][1] , I was unable to find a suitable approach. Perhaps I just missed it (that's to say, I'll be happy to read through more documentation if you know some that describes what I need). LXC version used is 2.20 (i.e. I'm using the LXD frontend).