1) Issue a letter to the CT-1 issuing authority requesting for cancelation of the CT-1 issued to u, with reasons thereof.
2) Send back the Machines with the dated acknowledged copy of the above said letter and canceled copy of CT-1 to the Vendor alongwith the received ARE-1/Invoice copy.
3) The vendor shall receive back the Machines with above documents.
4) The vendor shall submit the above documents and intimate the Range office about return of the machines and elaborate the necessity for carrying out modifications in the machines.
5) Range officer verify the machines with marks and nos on it and tally with the details from the Invoice/ARE 1 copy. He can also verify the LR copy for clearance and receipt of the machines as well the Ledgers.
6) After cancelation of the CT -1, you may take re-credit of the duty amount deducted from Bond Balance for such export.
7) Get a fresh CT -1 issued as and when the machine is ready at vendors place, after necessary modifications.
You may also sent and thereafter receive the same machine back after modification on the same CT-1, but it is advisable to follow about procedure.
You may also contact the CT-1 issuing authority for necessary guidance in the matter.