custom template

Hi, I want to create a custom container. I have installed some packages into the container and I made it ready for use but which files I need to change in my custom-container with original container files? For example; another?

With LXD one can take a snapshot and then easily use that snapshot to create a new template. You can do the same with proxmox, backup and then restore to create a new container, but then you have to change network settings and so on afterwards. Is there a super simple way to just add a current...