Hi Nick! If I understand your question correctly, the answer is probably No.

For domestic travel, if you are a DL elite, you can log in with your FF# and specify upgradeable (K or higher fares), or "lowest available" which usually means Not Upgradeable (L or U = LUser fares). For international travel, one can't even do that.
What's the deal with a specific fare class? Give us more details and we might be able to help more.

Check out the Flyers' Guide (link below) for more DL information.

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The Delta Flyers' Guide
E-mail on the Flyers' Guide site