Yup, £102/hour where my car was. It's one reason why I will probably take my car to an Indy in future. Outside of fixed price servicing the 'value' is questionable imo.
You will have to authorise the diagnostic work. I asked them to go straight to the Tensioner inspection but the dealer stated that they had to follow the exact procedure detailed in the TPI's that VW issue.
Power mods don't affect this particular component but it wouldn't surprise me if they used it as an excuse not to pay for a new engine and that would be where you would need to seek advice on the matter.