I often hear phrases like code freeze, version freeze but never heard of frozen being used in this context.
In modern software Version is often associated with Snapshot, Tag or Release. Version cannot be modified, you'll often find MD5 checksum for version releases. Phrase "version freeze" does not make much sense to me, but probably is used to describe pre-release feature freeze.
If you are working with "code branches" then you could say "code in this branch is frozen".
So as long as you apply "frozen" to the correct noun - specification, code, feature - it should be ok.