This is actually quite a significant technical achievement - for example, a similar project in Japan failed.

Japanese Railways wanted to build a train that can run at full speed (~300 km/h) on the standard gauge (1435 mm) regular Shinkansen lines but also use the narrow gauge (1067 mm) existing lines at slower speed. Those older lines would not have to be rebuilt for the Shinkansen standard & there would still be significant time savings:

https://en.wikipedia.org/wiki/Gauge_Change_Train

This failed to produce a viable train, resulting in falling back to track rebuilds or using relay trains that connect directly from Shinkansen to the local rail line on the same platform.

Swiss trains can, but while stopped.

There's a station on the main line that loads full sized cars with tanks on them onto little bougies that take them up into the mountains for training.