He has no choice. Impossible to fight the charge, as it’s a matter of incontrovertible fact not open to nuances of interpretation.
Deal already done. Clinesmith will have rolled on those who put him up to it: it’s unlikely that he altered the document except as part of a wider operation in progress.
What’s most interesting in the indictment is that the Crossfire Hurricane team had long possessed the C_A documents referred to - getting on for a year - and yet the SSA was unaware of the fact. Certainly indicates that the documents were withheld from operational agents by the FBI head office, and implies that the SSA was not in the loop of the general “Fuck Flynn” conspiracy.