89% of heart transplant recipients report personality changes https://www.mdpi.com/2673-3943/5/1/2
Hormonal changes can cause big changes in mood/personality (think menopause or a big injury to testicles).
So I don't think it's as clear cut that the brain is most of personality.
Neuromodulators like the hormones you're referring to affect your mood only insofar as they interact with neurons. Things like competitive antagonists can cancel out the effects of neuromodulators that are nevertheless present in your blood.
The heart transplant thing is interesting. I wonder what's going on there.
Sure but that has no bearing whatsoever on computational theory of mind.