https://www.ecfr.gov/current/title-32/subtitle-B/chapter-XX
And the various parts and sub-parts there, appear to be Federal Regulations - the law.
There are procedures left to the NARA, that are not yet clear, but in general, since Obama issuing some Executive Orders on the matter, specifically the marking of what is Declassified, may apply in Trump’s case.
Yet, no reason for the government to get excited about that. It is an administrative matter that could be resolved between the NARA and former President Trump, without all the Dept. of Justice theatrics.
https://wcl.american.libguides.com/c.php?g=563256&p=3877994
“These rules are considered legally binding just as any statute.”