I wasn't sure, but I don't like saying "no" without at least trying to determine why not. I checked with someone at Defense Pricing and Contracting who is familiar with FMS. Rather than there being a blanket prohibition, I was informed this issue is tied to the scope, purpose, funding, and statutory authority of the specific contract. Your question can best be answered by reviewing the terms and ordering conditions of the actual contract. To do so, you will need to contact the contract officer/specialist who administers it. Good luck, and I hope this helps.