It's not a custom map as such, but you can request changes to the stock map - for example you can have a stronger top end, or reduce torque between certain revs. Simon doesn't alter the maps himself, he sends the requests to Upsolute and they send him back the revised map.
I had my Passat done by Simon, and I wanted to be absolutely sure my clutch wouldn't slip (didn't want to fork out for a new one, and existing one is quite old) so had the torque pegged back between 2000-3000rpm.
Peak power at the upper end of the rev range remained unchanged, and I achieved 175bhp at the Awesome RR day, not bad considering the engine is on ~130k miles.