O ator que interpreta um capitão da nave é raptado por alienígenas reais

O romance é "Diplomatic Act", de Peter Jurasik & William H. Keith Jr. copyright 1998.

Richard Faraday didn't believe in aliens, even though he played one on TV. Unfortunately, the aliens believe in him ... or rather, they believe in Harmon, the alien diplomat Faraday plays on the SF program Star Peace. A war is threatening to tear the civilized galaxy apart, and only a diplomat as superb as Harmon can stop it. The problem is that the real aliens are just a little confused about the bizarre human concept known as fiction. They think Harmon is real....Well, real or not, "Harmon" had better solve their alien problems fast or Faraday, galactic civilization and Earth itself will be abruptly canceled.

Um bom romance que é muito semelhante e lançado um ano antes do romance / filme Galaxy Quest.

Embora não seja uma combinação perfeita, talvez a novelização do filme de 1999 Galaxy Quest?

"Em novembro de 1999, o Galaxy Quest foi romanceado pelo escritor de ficção científica Terry Bisson, que ficou muito próximo do enredo do filme."

Pontos correspondentes:

Leia um livro há 20 anos.

Check. 1999.

É sobre um ator que interpreta um capitão da série nesta série como o Star Trek

Check. Tim Allen plays Jason Nesmith a.k.a. (Cmdr. Peter Quincy Taggart) from the fictional show Galaxy Quest on the ship the NSEA Protector. Galaxy Quest is a loose Star Trek parody.

quem é sequestrado por alienígenas reais

Check. Unaware that they are truly octopoidal aliens, using technology to appear human, the barely conscious Nesmith is oblivious to his limo being beamed aboard the Thermian's spaceship.

e eles o substituem na Terra por um Android. Eles também o colocaram em uma máquina que consertou seu corpo no nível molecular.

No match. I don't remember this from the movie though it has been a few years. However, perhaps this might be related to the scene in which Allen as Commander Taggart is molecularly transported back to Earth? Or, perhaps the novelization might have deviated just a bit from the movie? As I recall, Allen's character was rather inebriated when he was kidnapped. Perhaps the Thermians had to sober him up quickly in the book.

O livro era ficção científica com humor.

Check. Galaxy Quest is a 1999 American comedy science fiction film directed by Dean Parisot and written by David Howard and Robert Gordon. Mark Johnson and Charles Newirth produced the film for DreamWorks.