Note that if you don't want to install mods, you can simply place two Metro stations on different lines next to each other and the Cims are more than happy to run up one flight of steps and down another one to change trains. You still have the problem of tunnels that need to cross over, but that's solvable. I put a small road in parallel with my main road, one station is placed on the main road, the other can go on the adjacent road and the two stations are basically touching.
I'm not sure what the limits are on how many times Cims will switch but i think so long as the total journey time doesn't get too long they're happy to do it. For example Bike-Metro-Train-Monorail-Bike commute.... Brompton folding bikes FTW.