I've also noticed that the rail replacement bus is tagged as a train route, its stops were not in order at the top of the relation, and it was not continuous (had gaps). 

https://www.openstreetmap.org/relation/19308543

I've since those issues in https://www.openstreetmap.org/changeset/168470267

It also appears that this arrangement will only last a few weeks? If it's temporary and short lived it doesn't need to be mapped as it can be hard to update it whenever it changes. The information will quickly become out of date. It does seem that this route is used quite a bit without it changing so it's probably fine to map, but it should have some description or conditional tag to show that it is in use temporarily and only under certain circumstances.

