Yes—they'll adjust the rate to the (much higher) one-way price. But there's no crazy "loss of use" fee like the parent comment suggested.

In practice, the cost usually turns into around $0.37/mile, plus the daily rate, unless you have a corporate discount.

When I talked to Enterprise on the phone about one-way use, they explicitly told me most places will waive the charge unless they don't have space to take the inventory. Rental car places have a lot of fixed capital costs like hotels, and renting the car at anything above a significant loss still recoups those costs. You can usually just ask for things. I've been offered upgrades pretty routinely just because they don't have the vehicle I asked for. They've always tried to charge me for the upgrade, but then I say "can you give me the rate I originally reserved?" and usually they give it to me.