apt-ftparchive(1) gives:
release
The release command generates a Release file from a directory
tree. It recursively searches the given directory for Packages,
Packages.gz, Packages.bz2, Sources, Sources.gz, Sources.bz2, Re‐
lease and md5sum.txt files. It then writes to stdout a Release
file containing an MD5 digest and SHA1 digest for each file.
Values for the additional metadata fields in the Release file
are taken from the corresponding variables under APT::FT‐
PArchive::Release, e.g. APT::FTPArchive::Release::Origin. The
supported fields are: Origin, Label, Suite, Version, Codename,
Date, Architectures, Components, Description.
See second paragraph. Perhaps a couple of "-o APT::FTPArchive::Xyz=Foo"
options could help?