My sympathies. We don't have as much overhead involved, but around integration time, it gets a lot like you're describing. We get away with a lot of common sense at other times.
More often, our enhancements get rolled into a new contract. If they are peripheral enough, we might not even do requirements for the new contract. Just using the old change requests is as specific as it gets.
It's actually not as bad as it sounds. Devs produce only a small amount of documentation (including unit test reports)--it's the product manager and QC department that really have the burden of documentation. It's nice having a well-defined set of requirements, and because of the overhead of updating documentation, scope creep is kept to a minimum.
More often, our enhancements get rolled into a new contract. If they are peripheral enough, we might not even do requirements for the new contract. Just using the old change requests is as specific as it gets.