In plain English
FAR 52.243-6, Change Order Accounting, is a contract clause prescribed at FAR 43.205(f), most recently dated Apr 1984. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 43.205(f), the contracting officer may insert a clause, substantially the same as follows:
Prescribing reference: FAR 43.205(f).
The official text, verbatim
As prescribed in 43.205(f), the contracting officer may insert a clause, substantially the same as follows:
Change Order Accounting (Apr 1984)
The Contracting Officer may require change order accounting whenever the estimated cost of a change or series of related changes exceeds $100,000. The Contractor, for each change or series of related changes, shall maintain separate accounts, by job order or other suitable accounting procedure, of all incurred segregable, direct costs (less allocable credits) of work, both changed and not changed, allocable to the change. The Contractor shall maintain such accounts until the parties agree to an equitable adjustment for the changes ordered by the Contracting Officer or the matter is conclusively disposed of in accordance with the Disputes clause.
(End of clause)