2013 Porsche Boxster

There is an open recall on my Porsche boxster, the Porsche recall number for this is AMC0. The recall involves reprogramming the car to reduce emissions in sport+ mode. My car has an aftermarket tune on the ECU, and the porsche dealership has told me that the recall is not possible due to this modification. If I want to get the recall done, they want me to pay to replace the ECU/DME. I also consented to and was charged for labor hours for the dealership to research any way to not replace the ecu and do this recall, but they found no method to do so. Are they legally allowed to refuse a recall due to modifications to the car? Should the cost to replace the ECU be covered under the recall? I can't seem to find any information about this online, so thanks for any information regarding this

HORN STICKS LOUD AND REMAINS ON FOR ABOUT ONE MINUTE. SUSPECT BRACKET HOLDING AIRBAG NEEDS NEW ISOLATION "O" RINGS WHICH, OVER TIME, ALLOW HORN TO TOUCH BRACKET COMPLETING HORN RELAY CIRCUIT. COULD CAUSE OTHER CARS TO SWERVE INTO TRAFFIC. SPECIFICALLY, I WAS STOPPED FOR A 4 WAY STOP SIGN, ANOTHER CAR APPROACHED AT SUCH A SPEED THAT I SAW SHE WAS GOING TO STOP AND SHE DIDN'T. I WATCHED HER BLOW BY AND GOT BEHIND HER AND BLEW THE HORN BUT THE HORN STAYED ON. THE LADY STOPPED AND I TOLD HER (SHE WAS A REALTOR GOING TO A SHOWING) SHE MISSED THE STOP. AS I WENT ON MY WAY THE HORN QUIT. TOTAL TIME 30-45 SECONDS. CONTACTING DEALER FOR REPAIR ESTIMATE.