As a Code Enforcement Official that has done permitting for multiple gen sets, my first question is- Where in the hell was your code official when this thing was installed, and secondly, where was the installer's head as the design and install were occurring?
1. First thing I always require- site plans, signed and sealed by a Design Professional (Architect or PE licensed in that state.) The plans must show where the set is to be placed in accordance with acceptable parameters set by the Manufacturer.
2. Second thing I require- a copy of the Manufacturer's installation manual (model-specific.) Must clearly show me where the set can be placed in accordance with windows, air intakes or other avenues where exhaust can enter the building.
Honestly I would be demanding someone's head on a platter (leaning very heaving towards the installer, they should know better......) but being 10 years later, you might be screwed. I would at the very least call the installer and discuss it with them- they may very well tell you to go bark at the moon, but if you start stomping your feet and advise them you may contact the manufacturer to tell them that the installer screwed the pooch big time, they may want to discuss it. Maybe have the municipal solicitor make the call. See if they will meet you halfway for the cost of relocating the pad and re-wiring it.
Oh, and since they screwed the pooch on the placement, have you had the wiring and transfer switch inspected by a third-party electrical underwriter? I know if I were you I would be making that call first thing Monday morning.