powermaster

If the command base is turned on the radio signal is pretty much in your house.  So the short answer is that the engine will respond to command control signals as long as there is enough voltage coming out of the Powermaster to run the trains.

I am talking about if say the legacy engine is in the round house and the conventional engine is on the main line will it respond as a conventional engine if the two tracks are hucked to gather.

As long as the legacy base is connected to the track and plugged in the legacy will sit idle until addressed and operated.

 If you disconnected or unplugged the base it would respond conventionally.

 I believe the legacy powermaster replaces the old TPC unit Lionel offered  and will allow for conventional and command operation on the same track at the same time.

Its not ideal operation as the legacy loco is limited to the voltage used for running the conventional engine, which conventional engines typically run at lower voltages. The lower voltage "hampers" the performance of the legacy loco, but I've tried it and it works.

One thing to consider is putting a siding on a toggle for your conventional engines where you could park them until you want to use them. When your ready you could switch the powermaster to conventional control  and then power up the siding and run your conventional loco.

The TMCC command signal is radio based.  It is pretty much everywhere in the house once you power up the command base.  The command/conventional switches on Powermaster and TPC's has nothing to do with signal propagation.  It has to do with the device running at fixed voltage.  

It is fairly difficult to force command controlled engines to run in conventional mode if a command base is connexted to the house wiring and turned on.

thank you