I checked internally. We would like to proceed as below.
You do not need to issue po twice but need to sign our sales contract .
1)Received PO from Simat : base on JPY and tentative ex-rate .
2)Sumitomo place order to Japan and issue sales contract in THB based actual ex-rate fixed.
3)Simat confirm our sales contract (sign back)
4)Sumitomo issue invoice follow 3)