Can the contractor's quote, as submitted with his subcontractor's quotes attached, be attached to the modification?
Very interesting situation.
When you read FAR 3.104 Procurement integrity, the definition of contractor bid and proposal information is found at FAR 3.104-1.
The prohibition on disclosing this information is found at FAR 3.104-4(a) “Except as specifically provided for in this subsection, no person or other entity may disclose contractor bid or proposal information or source selection information to any person other than a person authorized, in accordance with applicable agency regulations or procedures, by the agency head or the contracting officer to receive such information."
Note: bold italics added for emphasis.
Because the prime is the one who provided it to you, attaching it to the modification seems like it would be ok (e.g. authorized person). However, caution should be taken because the contract modification will be distributed and it is harder to control what or who will see the modification afterwards. Example, the prime may show the modification to a different subcontractor after it’s distributed. While technically not your fault or issue, this could lead to a headache.
Therefore, we strongly recommend asking the prime contractor to get permission from the subcontractor prior to doing this. Or redact proprietary information if marked and only use the information that’s absolutely necessary for the contractor to do the work as modified, or just reference the quote in the modification.