Such a release would not be handled as a matter of copyright infringement or IP, but a s a matter of a violation of secrecy laws. In particular, if it is claimed that some of the content would imperil national security if made public, it could be classified, and unauthorized release would be a crime. This was the claim made in the famous Pentagon Papers case.
Indeed, as a comment points out, the report is a "work of the United States Government" because it was created by government employees (Muller and his staff) within the scope of their employment. As such it is totally ineligible for copyright under US law.
Also, if some of the redactions are present to protect the privacy of individuals, there would be an issue with the violation of laws protecting individual privacy.
If some of the redacted content is Grand Jury testimony (as appears rom news reports to be the case) The Federal Rules of Civil procedure 6 provide for secrecy until a court authorizes release, specifically rule 6(e)(2)(B). Disclosures may be authorized by the court, may be made under various provisions of rule 6, or may be authorized by 18 U.S.C. ยง3322.
There might be other laws involved as well, depending on the reasons why various content has been redacted.
Even in a copyright case, where "parody" is relevant to the issue of fair use (under US law), it is not enough to just call something a parody. It must actually be a parody. That is to say it must be a modified version of the original used to mock or comment on the original, or in some cases to comment on other issues. A parody in this sense is always a transformative use.
If the content present in place of the redacted sections were accurate, or even appeared reasonable to one not knowing the true content, it would be unlikely to be accepted as a "parody". If on the other hand the released content showed that the president's campaign team met with Donald Duck, and this was disclosed to their opponents by Batman, that would be a fairly obvious parody, perhaps commenting on taking trivial matters over seriously.
If an unauthorized person were to release what purported to be an unredacted version of the report, legal action might or might not be taken, but if it were it would not be likely to be on the basis of copyright infringement.
This answer concerns what would or might happen if someone were to publish the actual report, or an invented report that appeared to be the actual report, not an invented version that was obviously untrue. When initially asked, that is what the question seemed to be about, and it is a situation which may be of interest to some. The OP has clarified that the question was about a clearly invented or fantasy version of the report. Only the sections of this answer about copyright not applying are relevant to that situation.
