I have bad news: You're Swampman.
Remember that hike you took last week by the swamp during the electrical storm? Well, one biological organism went in, but a different one came out. The "[your name here]" who went in was struck and killed by lightning. Simultaneously, through freak quantum chance, a molecule-for-molecule similar being randomly congealed from the swamp. Soon after, the recently congealed being ran to a certain parked car, pulling key-shaped pieces of metal from its pocket that by amazing coincidence fit the car's ignition, and drove away. Later that evening, sounds came out of its mouth that its nearby "friends" interpreted as meaning "Wow, that lightning bolt almost hit me in the swamp. How lucky I was!" Lucky indeed, but a much stranger kind of luck than they supposed!
So you're Swampman. Should you care?
Should you think: I came into existence only a week ago. I never had the childhood I thought I had, never did all those things I thought I did, hardly know any of the people I thought I knew! All that is delusion! How horrible!
Or should you think: Meh, whatevs.
Option 1: Yes, you should care. If it turns out that certain philosophers are correct and you (now) are not metaphysically the same person as that being who first parked the car by the swamp, then O. M. G.!
Option 2a: No, you shouldn't care, because that was just a fun little body exchange last week. The same person went into the swamp as came out. Disappointingly, the procedure didn't seem to clear your acne, though.
Option 2b: No, you shouldn't care, because even if technically you're not the same person as the one who first drove to the swamp, you and that earlier person share everything that matters. Same friends, same job, same values, same (seeming-)memories....
Option 3: Your call. If you choose to regard yourself as one week old, then you are correct in doing so. If you choose to regard yourself as much older than that, then you are equally correct in doing so.
Let's call that third option voluntarism about personal identity. Across a certain range of cases, you are who you choose to be.
Social identities are to a certain extent voluntaristic. You can choose to identify as a political conservative or a political liberal. You can choose to identify, or not identify, with a piece of your ethnic heritage. You can choose to identify, or not identify, as a philosopher or as a Christian. There are limits: If you have no Pakistani heritage or upbringing, you can't just one day suddenly decide to be Pakistani and thereby make it true that you are. Similarly if your heritage and upbringing have been entirely Pakistani to this day, you probably can't just instantly shed your Pakistanihood. But in vague, in-betweenish cases, there's room for choice and making it so.
I propose taking the same approach to personal identity in the stricter metaphysical sense: What makes you the same being, or not, in philosophical puzzle cases where intuitions pull both ways, depends to a substantial extent on how you choose to view the matter; and different people could legitimately arrive at different choices, thus shaping the metaphysical facts (the actual metaphysical facts) to suit them.
Consider some other stock cases from the literature on personal identity:
Teleporter: On Earth there is a device that will destroy your body and beam detailed information about it to Mars. On Mars another device will use that information to create a duplicate body from local materials. Is this harmless teleportation or terrible death-and-duplication? On a voluntaristic view, that would depend on how it is viewed by the participant(s). Also: How similar must the duplicate body be for it a qualify as a successful teleportation? That too, could depend on participant attitude.
Fission: Your brain will be extracted, cut into two, and housed in two new bodies. The procedure, though damaging and traumatic, is such that if only one half of your brain were to be extracted, and the other half destroyed, everyone would agree that you survived. But instead, there will now be two beings, presumably distinct, who both see themselves as "you". Perhaps whether this should count as death or instead as fissioning-with-survival depends on your attitude going in and the attitudes of the beings coming out.
Amnesia: Longevity treatments are developed so that your body won't die, but in four hundred years the resulting being will have no memory whatsoever of anything that happened in your lifetime so far, and if she has similar values and attitudes it will only be by chance. Is that being still "you"? How much amnesia and change can "you" survive without becoming strictly and literally (and not just metaphorically or loosely) a different person? Again, this might depend on the various attitudes about amnesia and identity of the person(s) at different temporal stages.
Here are two thoughts in support of voluntarism about personal identity:
(1.) If I try to imagine these cases as actual, I don't find myself urgently wondering about the resolution of these metaphysical debates, thinking of my very death or survival as turning upon how the metaphysical arguments play out. It's not like being told that if a just-tossed die has landed on 6 then tomorrow I will be shot, which will make me desperately curious about whether the die did land on 6. It seems to me that I can, to some extent, choose how to conceptualize these cases.
(2.) "Person" is an ordinary, folk concept arising from a context lacking Swampman, teleporter, fission, and (that type of) amensia cases, so the concept of personhood might be expected to be somewhat indeterminate in its application to such cases. And since important features of personhood depend in part on the person in question thinking of the past or future self as "me" -- feeling regrets about the past, planning prudently for the future -- such indeterminacy might be partly resolved by the person's own decisions about the boundaries of her regrets, prudential planning, etc.
Even accepting all this, I'm not sure how far I can go with it. I don't think I can decide to be a coffee mug and thereby make it true that I am a coffee mug, nor that I can decide to be one of my students and thereby make it so. Can I decide that I am not that 15-year-old named "Eric" who wore the funny shirts in the 1980s, thereby making it true that I am not really metaphysically the same person, while my sister just as legitimately decides the opposite, that she is the same person as her 15-year-old self? Can the Dalai Lama and some future child (together, but at a temporal distance) decide that they are metaphysically the same person, if enough else goes along with that?
(For a version of that last scenario, see "A Somewhat Impractical Plan for Immortality" (Apr. 22, 2013) and my forthcoming story "The Dauphin's Metaphysics" (available on request).)