Simplest thing is yes legacy and TMCC locomotives can be “shut down” that is key 5 on the Cab-1 or 2. On the Cab-2 you can also hit ENG where you would select the ENG number and on the bottom right you’ll see the power button and stop sign button. That also gives you the ability to restart the locomotives. Keep in mind that in TMCC and early Legacy all this really does is shut down the sounds all the lights stay on. Newer Legacy the only thing that Will stay on is the number boards. Toggle switches on sidings is a very typical thing most add to their layout. While there isn’t anything “wrong” with leaving locomotives powered the more time the electronics are active the sooner there’s a possibility of something failing. And if there’s a row of passenger cars they can pull some power 😉.
Lionel locomotives won’t know a difference when power is shut off and comes back on. As long as there is a command signal they will be silent until addressed. DCS locomotives on the other hand will only be silent if they see the Watch dog signal from a TIU or explorer. This is only put out when power of first applied to that output so in this case sounds will immediately come on in your siding scenario. The smart people on here found how to take a RC commander and make it continuously send out the watch dog signal so that all DCS locomotives stay silent. Just look up PWD (Perpetual Watch Dog) signal generator on the forum
