It would be nice to bring back the old tunnels in the new version but it would be better if you could choose which type of tunnel to use AND for you to merge tunnels for double track
I don’t think there is a way to bring back the old tunnels but it would be nice 😉
At the moment you can not. But when the great people that make things for RTR get round to making different tunnels you can use the turn off auto tunnel button to use them. Just like the Bridges