I am looking to recall a book I read 20 years ago.
A journalist/anthropologist man (human) studies aliens.
He uses various techniques to get close to hard to study aliens.
He starts to use tech to modify his body so he can get closer to the aliens or study them better.
By the end of the book his body is so modified he no longer sees himself as human, and indeed has more or less forgotten his human roots.
It was in English.
"by the end of the book" he was modified and no longer saw himself as human (ergo... nothing happened after that, that was the end of the book).
His motivations are (journalist/anthropologist) he was there to simply study the aliens (there may have side stuff to that plot, I forget).
How he modified himself (to the best of my memory) = technology. (surgery, and part grafting and other I do not recall).
What he learned from the aliens (their physiology and culture).
Where was he studying them? = On their home worlds.
How did he get access to them? = I don't fully recall (space flight seemed to be a thing, but unimportant to the plot).
Was their presence known to other humans? (Sorta, kinda like Jane Goodall, he would go find new species and study them, I don't recall how the rest of the books universe heard of the aliens.)
It was a standalone book, not a part of a series.
It was fairly short, maybe... 350 pages or so.
Each chapter showed the protagonist's mind having slightly more trouble with human concepts or speech patters.
It is somewhat like reading the protagonists' 'journal'.