This response is based on the information provided.  We suggest you discuss with your contracting team, program manager and/or legal department as appropriate. 

We understand the contract, is an IDIQ contract and the unit wants to increase the dollar threshold as the vehicle is being used at a more rapid pace than originally projected.  The existing IDIQ contract was an "Other Than Full and Open Competition" using FAR 6.302-3 as its basis.   To increase the dollar threshold without initiating a new competition you need a justification and approval (J&A).  The good news is that the unit already has an approved J&A.  None of the requirements have changed, but the magnitude of access has grown beyond original projections.  We would find it hard to justify any other justification than the one presented in the initial award. As nothing has changed from the original requirement, how would the basis of justification change.  Not only might that be more difficult to argue during the internal process, but the government is more open to industry challenge for changing the basis of reducing competition. 

As for synopsizing, we believe it is not necessary based on your situation and the exceptions at FAR 5.202(a)10 and (11).