Is it obligatory for someone named "Abd al-Muttalib" to continue with this name, or is it incumbent upon him to change it? And is he sinful for bearing this name throughout the past 49 years?

If it is possible to change the name of servitude to other than Allah in official documents, then let it be done. Otherwise, let it be changed in interactions with people, for Allah Almighty says: {So fear Allah as much as you are able}.