My name is XXXXX XXXXX your exhaust system work would not effect the odometer operation. The speedo and the odometer receive the signal from the same wire. The odometer motor is defective and the only repair is to replace the speedometer head. If this info is helpful please select ACCEPT. If you need more info just ask and Ill just answer. Remember me with your next honda question and FEEDBACK, it is important.
The cost ranges from a couple hundred new to less than a hundred for used plus labor. Most likely this will not effect speedometer operation and if you dont plan on selling the car it probably wont matter.