IIRC, the Sheffield ones can operate on either the tram-train (Cathedral to Rotherham) or the Supertram network, they cannot do both. Of the seven, I think four are for tram-train and three for Supertram, I don't know the current allocations. The reason is there are different bogies for the two systems (flange depth I think) so they have to lift them and change the bogies if they want to swap any around (IE accidents).
I don't know, but it's possible there are different light settings that are changed over in the workshop. The only bit of the tram-train that is street running is Commercial St to Cathedral and that's pedestrianised with a couple of road crossings.