Extreme evidence of time line manipulation

We watched it during class in my latter high school days, i graduated in 2003 and we indeed watched a movie about Kevin Costner hears a voice telling him to build a baseball diamond in his cornfield an that people would come from all around to see it and as he was doubting the voice told him "if you build it they will come" meaning the people would come and he can save his farm or whatever. So he like the OP says works effortlessly to make the diamond and suceeds and it ends with a large crowd of people there watching the dead baseball players.

This is how i have always known this movie and i was horrified to find out that it is completely different just a few short months ago

I just posted about this so-called "Mandela Effect" on Youtube. Here's what I wrote:

You remember things misspelled because, in most cases, the real spellings are different from how they "should" be spelled and you simply didn't pay attention. E.g., "Cap'n Crunch": It's pronounced "Captain Crunch," it's mentally remembered as sounding like that, so, therefore, you assume it's actually spelled that way without really looking at the cereal box to find out.

The movie quotes: They're misremembered because a) they become popularized through some comedian or talk-show host riffing on it incorrectly, and it's the mis-memory that is remembered, or b) they become generalized ("build it and they will come" is now a line used to encourage someone to do something, so saying "build it and HE will come" makes zero sense to say. Or "Life is like a box of chocolates" is just a way of saying that life is full of surprises. It makes no sense to say "Life WAS like a box of chocolates" to someone to indicate that life can throw some curve balls. In the Gump movie, however, Hanks's character is mentally challenged and speaks in a way that reflects that fact. When you're talking to a friend and trying to indicate that life is full or twists and turns, you are speaking in the present tense and are, presumably, speaking normally. So *you'd* say that life IS like a box of chocolates. Since "life is like a box of chocolates" and "build it and they will come" are the phrases most often heard after a quote has become generalized, people mis-remember "having heard" those lines spoken that way in the original movies as well.

So, you go through a website and see page after page of mis-memories, and then feel as if you can't trust your instincts when, in fact, there's nothing wrong with you or your instincts or your memories. You simply weren't paying enough attention in the first place, and remembered things incorrectly for logical, sane reasons. There is no "parallel universe." The fabric of space-time is just fine. God is in His Heaven and all is right with the world.

--- but it's fun to see these mis-memories all in one place! So I'm glad that the "Mandela Effect" idea is out there for that reason. I just wish people would think more logically about it all and not freak themselves out over it.

Yes! I was positive it was if you build it "they" will come. I watched this movie loads of times as a kid and im sure it was "they". Even in some other movies that reference it or make fun of it im sure they say "they". I cant remember exactly which ones. But I do remember one episode of married with children where Bud builds a wormhole gate in his basement. Im sure he says "they". But this is all just memory. And memory is the worst possible witness of anything. Witnesses to crimes have sworn it was a blue car and it was bright red. Memory is just too vague. Even some dreams over time can become "memory". Reading about the mandela effect now its very interesting.

Yes, this is how most people remember the movie. "If you build it, they will come" is the original line and the way I know it. The changes are what we (those who see the changes) call Mandela Effect. Field of Dreams is not the only movie to be "effected." Moonraker has changed, as has Risky Business. Jaws, Terminator, Apollo 13 and many others. As well as books, names and product logos. Look into Mandela Effect for more info.

Discussion of timelines & timeline manipulation is utterly beside the point with this film. It's fable & parable, not science-fiction. It's one with many works of poetry & literature across the centuries in which people hear voices, see visions, and are given a mission with increasingly more difficult tasks to test their willingness & belief. In this regard, it has a lot in common with Close Encounters of the Third Kind, as Roy Neary is similarly touched by a vision from on high & pursues it despite every obstacle in his way. Roger Ebert was right in his initial review of it: this is a religious picture, but the religion is baseball. And baseball is the framework for its story about faith & redemption for all of its characters.

Here's a reference to it closer to when it was released. I'm not sure how anyone can explain this away. I saw it when it came out. All anyone has ever said in reference to the film is "they" will come.
https://youtu.be/9ArIs8R1aAo?t=176
There was a longer clip of this, but I don't see it.