I was thinking it was the parents that assigned the different surname when naming their newborns, not the children that threw the name away. The former sounds legally easier than the latter.

My question was, why assign a lower-caste name to one's child if they have the option not to? But I suppose even then not all people with these lower-caste names see their surname as bad or harmful to their children, if I understood you correctly.

For Reservations

No. Caste based reservation is not tied to your surname. Major chunk of population of Kerala and Tamil Nadu don't have a caste related surname. It doesn't make them ineligible for caste based reservation. Because the point of the reservation is to level up these communities from the descrimation they faced for hundreds of years. Just changing the caste name doesn't automatically level the playing field. It helps. But they need more support as well.