“It will be possible to add platforms (parallel to the existing ones) to a station, but only within limits that depend on the station type”
So we will have to demolish the small station and build a new, large station. Presumably this means that the (gone) small station will be expunged from all lines in which it was used, and a new large station will have to be added manually to them all. Right?
Moral: build a small large station from the start, and expand it!