hascelebrated its 55th birthday on 17 July 2010.
A past time is mentioned, so we need a past tense.
2) An amazing 500spacemillion people have
sincevisited the theme park since that date.
cCartoon Cars ha sve become one of the most famous and well-known brands all over the world.
hascreated everything from scratch. He's dead, so we need a past tense.
7) While the idea of improving the pleasure has not changed, the company has revamped its ticketing prices and policies.
I am not sure what you mean by 'improving the pleasure'. There seems to be no real contrast here, so this sentence, beginning with 'while' sounds strange.
Student or Learner