The FISA applications in question are even more egregious, because I'd say there's a damn good possibility that the FBI did everything according to the letter of the law even if their intentions were nefarious. For example, if they knew the Steele dossier was fake but used it to get FISA warrants, then the FISA warrant applications themselves might have been perfectly "legal" if they simply cited the dossier verbatim and identified its source.
Good questions, but they are official records, at a minimum, and falsely modifying or submitting official records of any kind in the DoJ is surely a crime, as there are many laws against just regular citizens falsifying government docs.