Why the name changes?
Why were character names changed between Parts 1 and 2?
Sara became Claire. I believe Melvin's last name was originally Ferd in Part 1 instead of Junko, but I could be wrong. It's been years since I've seen either movie.
In the trivia section, it says:
"Melvin's last name was changed from Ferd (as it was in the original) to Junko for the sequels, in order to explain his Japanese heritage for the plot of the movie."
I have no idea why they changed Sara's name to Claire.
My Top 100: http://www.imdb.com/list/ls073432147/