...and then he puts himself back together again.

His own opinion is that you couldn't really call the result 'Keltham'.  If you take a lifetime of experience at INT-18/WIS-16/CHA-14 and pour the result into a mind of INT-25/WIS-26/CHA-25, it's a bit like pouring the contents of a four-year-old into an eighteen-year-old.  The numbers skip over a lot of important detail.  Golarion's abilitystats may not really be thinkoomph but they sure are some major subdimensions of it.

He is putting the traumatized pieces of that four-year-old back together as best as he can, improvising psychiatry skills that he was never taught because you can just do that at 25/26/25 if you have enough of the underlying knowledge.

But it's still a four-year-old being poured into something much larger than a four-year-old, with rapidly cascading knowledge and insights that contradict a lot of what did go into that four-year-old.  At some point there's not that much difference between making the new person out of Keltham-who-was and just making them out of a generic dath ilani with the same abilitystats.

...he still tries as hard as he can to make the new person be Keltham+, not just the + of a generic dath ilani with the same abilitystats.

There's a lot of reasons to do it that way, and no particular metareason to single out any particular one as the justification.

...and then he puts himself back together again.

His own opinion is that you couldn't really call the result 'Keltham'.  If you take a lifetime of experience at INT-18/WIS-16/CHA-14 and pour the result into a mind of INT-25/WIS-26/CHA-25, it's a bit like pouring the contents of a four-year-old into an eighteen-year-old.  The numbers skip over a lot of important detail.  Golarion's abilitystats may not really be thinkoomph but they sure are some major subdimensions of it.

He is putting the traumatized pieces of that four-year-old back together as best as he can, improvising psychiatry skills that he was never taught because you can just do that at 25/26/25 if you have enough of the underlying knowledge.  (He could have reinvented psychiatry eventually, as he was before, but not quickly.)

But it's still a four-year-old being poured into something much larger than a four-year-old, with rapidly cascading knowledge and insights that contradict a lot of what did go into that four-year-old.  At some point there's not that much difference between making the new person out of Keltham-who-was and just making them out of a generic dath ilani with the same abilitystats.

...he still tries as hard as he can to make the new person be Keltham+, not just the + of a generic dath ilani with the same abilitystats.

There's a lot of reasons to do it that way, and no particular metareason to single out any particular reason as the justification.

...and then he puts himself back together again.

His own opinion is that you couldn't really call the result 'Keltham'.  If you take a short lifetime of experience at INT-18/WIS-16/CHA-14 and pour the result into a mind of INT-25/WIS-26/CHA-25, it's a bit like pouring the contents of a four-year-old into an eighteen-year-old container.  The numbers skip over a lot of important detail.  Golarion's abilitystats may not really be thinkoomph but they sure are some major subdimensions of it.

He is putting the traumatized pieces of that four-year-old back together as best as he can, improvising psychiatry skills that he was never taught because you can just do that at 25/26/25 if you have enough of the underlying knowledge.  (He could have reinvented psychiatry eventually, as he was before, but not quickly.)

But it's still a four-year-old being poured into something much larger than a four-year-old, with rapidly cascading knowledge and insights that contradict a lot of what did go into that four-year-old.  At some point there's not that much difference between making the new person out of Keltham-who-was and just making them out of a generic dath ilani with the same abilitystats.

...he still tries as hard as he can to make the new person be Keltham+, not just the + of a generic dath ilani with the same abilitystats.

There's a lot of reasons to do it that way, and no particular metareason to single out any particular reason as the justification.