No, the Agent version must match the base code version
If you contact Veritas, you should be able to explain the situation, provide the v10 serial and be provided with a v9.1 serial
The way that Veritas/Symantec is going tho, this may not work any more
You could also check EBay or the other Auction or Surplus sites and see if you can find a 9.1 Exchange serial for sale, and return the v10 to CDW (Who should have verified your base level before selling you the Agent)