McLaren will be making some rolling changes to its MP4-12C supercar later this year and has informed existing customers that the changes can be retrofitted to their cars, at no additional cost.

This is the second time that McLaren is updating the MP4-12C post launch, the previous change was due to some software bugs that affected some of the car’s electronic systems.

The latest updates are the kind we prefer--more power under the hood.

In a letter sent out to existing customers, McLaren managing director Antony Sheriff has revealed that output will be increased by 25 PS (approximately 24.6 horsepower) to give the MP4-12C a final output of 616 horsepower.

Letter sent to customers by McLaren managing director Antony Sheriff

Letter sent to customers by McLaren managing director Antony Sheriff

A scan of one of the letters, which was posted on the website McLarenDriver, has been reproduced here.

According to the letter, the increased output is courtesy of a remapping of the engine’s ECU. Importantly, the car’s fuel economy figures remain unchanged, which means it will still escape the gas guzzler tax.

In addition to the increased output, McLaren will also be making some changes requested by customers. These include remote opening of the passenger door, a programmable engine note, enhanced equalization options on the Meridian surround sound system and an upgraded IRIS infotainment system.

Existing owners will be able to have all the upgrades installed free of charge at their local McLaren dealer in October of this year.

The introduction of the changes is scheduled to coincide with the launch of the McLaren MP4-12C Spider, which has been spied testing for over a year now and is set for a debut at the 2012 Bebble Beach Concours d'Elegance in August.