Good Luck with your first job Bathpool. I'm in a similar position to you - 4 months post training!! But I would always try to remove, and warn them it could get damaged if the screws are old and rusty.
One of my first quotes was for someone who was getting a new bathroom fitted and wanted me to tile it. I mentioned about removing the new toilet and sink, and she asked me not to. I explained I prefer to, otherwise it can take longer to get the cuts right around the WC Pan/Pedestal, and it never looks as good as the sanitarywear sitting on top of the tiles etc,etc, and easier to get a nice seal. Surprisingly - I didn't get the job!
It can normally be done fairly painlessly by adding some flexible hoses to the water supplies (10 or 15mm), try to make sure they have a decent bore size though. The 110 waste pipe can normally be dealt with by adding an offset pan connector. It's normally the 32mm or 40mm waste's that can be a bit difficult to re-route as a 10-20mm change in height is usually too much for a couple of offsets (45 deg bends). So I guess you could try flexible waste pipe connectors, if the solid pipe needs to be moved.
You'll have to weight it up yourself unless you did some pictures. Exactly what you need depends on current pipe layout!