To be honest, I don't think you can do that. As far as I know. I'd be nice though, because it can be a drag to see the same stuff over and over. Just my thoughs.
It does not have "Content Manager". I did some more searching on it and its a Module version/release for Trainz 06. It can't be expanded with new content. Only the routes, with assigned engines can be used. Well at least I bought a newer version of Trainz on Ebay a few days ago.