No, it is not possible to replace a single gear on a cassette. The gears on a cassette are typically designed as a single unit and are not intended to be individually replaced. The cassette is a cluster of multiple gears that are mounted on a freehub body of a rear wheel.
If a gear on the cassette is worn out or damaged, it is necessary to replace the entire cassette as a unit. This ensures proper functioning and compatibility of the gears, as they are designed to work together as a set. Replacing the entire cassette allows for a smooth and efficient gear shifting performance.
When replacing a cassette, it is important to choose a compatible cassette that matches the number of gears on your bike's drivetrain. Additionally, it may be necessary to adjust the rear derailleur and potentially replace the chain if it has also experienced wear or elongation.
It's recommended to consult a professional bicycle mechanic or a knowledgeable bike shop to assist with the proper selection and installation of a new cassette, as they have the expertise and tools to ensure a smooth and reliable replacement process.