I believe the OP was wondering whether the pump could be permanently disabled and ONLY run pre-mix. I haven't looked closely enough at my "new to me" DT175 to see exactly where the injection oil is delivered. If it is only delivered in the intake stream, after the carburetor, (ie Yamaha Autolube) it should be possible to eliminate the pump completely and permanently. If it is delivered to any other point, such as a main bearing first, (ie Suzuki Posi Lube) then the pump can never be by passed or disconnected without eventual permanent damage to the engine.
Anybody got the quick answer to the delivery point for the injection oil?