The original story focused solely on an alien living in a forest, trying to overcome his isolation and find out where he came from. Lilo didn’t become a part of the film until much later during story development.
The filmmakers considered setting the story in rural Kentucky or Kansas before finally settling on Hawaii.
Stitch was not originally supposed to talk, but when the filmmakers realized the story hinged on him being able to express himself at the film’s end, they began developing his voice. Director Chris Sanders provided Stitch’s voice during test animation, and eventually everyone got so used to it that they decided to keep it.
Stitch was originally supposed to the leader of an intergalactic gang, and Jumba was supposed to be his former partner who was sent to earth to find him. The filmmakers eventually decided to make Stitch a genetic mutation instead.
In the same vein, Lilo was supposed to remind Stitch of what he was like before he became an intergalactic criminal, and inspire him to regain his innocence and goodness.
After an early test screening showed that audiences thought Nani was Lilo’s mother, filmmakers reworked some key scenes to make their sisterly relationship clear.
Lilo & Stitch was the first Disney animated film since Dumbo to use watercolor painted backgrounds.
The film had special premieres in Honolulu and in Graceland.
While on a tour of Kauaʻi, filmmakers noticed that their Hawaiian tour guide seemed to know someone everywhere they went. They were so struck by the guide’s explanation of the term “‘ohana” as it relates to an extended family, that they made it the central theme of the film.
Lilo & Stitch was the first feature length animated film to be set in Hawaii.
Tia Carrere and Jason Scott Lee (who voiced Nani and David) helped rewrite their characters’ dialogue using correct Hawaiian colloquialisms and slang.
References
https://ohmy.disney.com/movies/2015/08/08/11-things-you-didnt-know-about-lilo-stitch/