I am working on a repeatable ISO build process, and with the help of one of the developers of Subiquity, we discovered (https://bugs.launchpad.net/subiquity/+bug/1937923) that there doesn’t appear to be any way for him to permit users to download arbitrary versions of snaps.
This is problematic, as each ISO that uses Snapcraft will pull the latest software, which is appealing to most individual desktop users, but is not tenable for fleet management of hundreds or thousands of machines.
The ability to pull specific versions of Snaps would be a large win for installations that need to manage state, as well as for things like regression testing.
Please consider putting this on the roadmap. Let me know if I can provide any additional input or help in any way?