Is it permissible for one who intended to perform Hajj this year, registered, and paid a portion of the fees, to change his intention to perform Hajj on behalf of a deceased relative?

It is permissible for a person to perform Hajj on behalf of another after having performed Hajj for themselves. They are not obligated to perform Hajj for themselves in that year merely by registering with a campaign and paying a portion of the fees. Indeed, even if they performed the Umrah of Tamattu' for themselves and then intended to perform Hajj on behalf of another, that would be permissible for them.