Yes, you can. Many people do. I have, though not on a TATL itinerary. The most recent, already a few years in the past, involved flying to the starting point of a one-way car rental that ended at my international point of entry.

In theory, this violates the conditions of the ticket. In theory, the airline could bill you the fare difference. In practice, they have (successfully) gone after travel agents who made a practice of booking cheap round trips for clients who needed one-way flights. The airline computers apparently figured out that an improbably high fraction of those agencies' round-trip tickets weren't being used in full. If an individual does it once in a while, no problem; there are many legitimate reasons for missing a flight.