I already saw that kind of questions but with no real answer. I'd like to build a Debian stretch installation media (with simple-cdd) that ships with stretch-backports packages. I could only go with adding the backports repository in the preseed configuration file but it wouldn't be usable with offline devices. Any idea ?
If you know how to generate list of packages just put it to
.downloads file. These packages, together with the dependencies, will be included into
/pool/main/ directory of resulting image
Actually, it seems there's no easy way (given the easy-way is simple-cdd) to fine tune the packages shipped with a debian installer media. One could actually customize its repository given it resolves all the dependencies one way or another. (see : Building a Custom CD Set)
However, for the particular backports case one could use in its simple-cdd configuration (profiles/[profile].conf) the parameters :