Well, to my understanding, nothing should change if you allready use SAP TM.
At 2.1.16.1 Transportation (LE-TRA) the Simplification List (v1.5) says that SAP TM is the future Transport Solution when using S/4 HANA
The Logistics Execution Transportation (LE-TRA) is not the target architecture within SAP S/4HANA,
on-premise edition 151158. The (already available) alternative functionality is Transportation Management (SAP TM).
hope this helps
Joachim