Is it permissible for me to change my family name to "Kalfan" (the original family name of my father and grandfather) instead of "Salfan" (the name my grandfather changed when he immigrated)?

There is no objection to changing a family name back to its original name, especially if there is a legitimate benefit, such as knowing one's lineage and maintaining kinship ties. However, two matters must be observed: that the change does not lead to the loss of people's rights, and that the children are informed of the change so they may know their relatives, avoid forbidden acts, and severing ties of kinship, in accordance with the saying of the Prophet, peace and blessings be upon him: "Learn enough of your lineages to maintain ties of kinship."