Translation:The character in the book has a different name.
Yes, this is spot on!
But you wouldn't use "forskellig" in the way that you describe though, if the character is named one thing in the book and another in the film we would use "andet".
"Karakteren har et andet navn i bogen." The character has another/a different name in the book."
But lets say the character starts out as named "Kim" and at the end of the book the name is "Sam", then you would use "forskellige".
"Karakteren har forskellige navne i bogen." - The character has different names in the book.