Looking for the title of a book about being stark raving mad to navigate a ship [duplicate]

Question

I once read a story about the future!

• Brain cybernetics were common. If you were "average" you got average brain implants. If you were wealthy you got the latest-and-greatest tech. It was illegal to replace implants (or add new tech) at a later age. One of the characters did so anyway (ended up being hired as a hacker for one of the major leaders in the book). He had a phrase like, "doc, you might as well just close my skull with a zipper 'cause I'll be back" or some such.

• Kids coming out of hypersleep/cryogenics would turn on their implants, which turned everyone walking around them into NPC characters in their games, and start running around playing games.

• The book had a strong theme about sanity, mental disorders, and how they were embraced productively rather than shunned socially. I remember an old guy who painstakingly re-drew his tattoos rather than having them permanently inked because it would drive him nuts seeing them go blurry with time (he also overfocused on his work and had to be told to eat, he drank something frothy).

• The protagonist was a multiple-personality. One of them was, well... randy. (Sorry, I'm a guy, we remember stuff like that.) Getting the multiple personalities to work one-with-another to get the protagonist out of trouble was a key theme in the story. One of the personalities was stark raving mad (considered socially to be a bad thing), but ended up being useful because the madness allowed her to see the dangers lurking in "hyperspace" (I'm not sure that was the word used) so navigators could avoid them. The madness of one of her personalities was critical in saving the ship near the end of the story.

At a guess, I read this back in the mid to late 90s.

Answer 1

On reflection, I suspect this is probably This Alien Shore by C.S. Friedman.

The book definitely explores the theme of what constitutes sanity, and the possible advantages of mental "disorders"; the Guerrans who run interstellar commerce have created an elaborate system of face painting that help describe the attributes of each person's psyche to others in a fairly standardized way.

The main protagonist is Jamisia Shido (approximately), who contains a number of largely independent subpersonalities. Katlyn is the seductress with an outsized libido. The last one to reveal itself in the novel is unnamed, but has the required "Outpilot Syndrome" required to navigate the ainniq (hyperspace); outside of navigation, he seems to be insane and effectively curls up in a corner of Jamisia's mind.

The other main viewpoint character is Phoenix, who is a modded hacker; he has had extra bioware added to his brain. (Every child is given brainware at birth, but it could be out of date or might not have grown optimally. Hackers illegally add extra bioware to augment their abilities.) He is 2 levels below the top Guild person in his group, but aims to get recognized and promoted.

I don't recall your middle 2 points, but there was one scene where a navigator (who has suffered a breakdown) is described as having scarification and tattoos all over his body.