One common designation given characters is that they are a "X, later Y" antagonist or villain such as "the main, later secondary villain". This is because their overall importance in the story appears to change as the story progresses. Sometimes, it's because new information shows another character's importance is higher or lower.
I recently saw a note by another person that said "movies don't suddenly change their minds. They have a set villain from the beginning, and what happened was a twist."
That's a good point to remember. By the time a movie starts filming or animating, everything has to be locked down and defined as much as possible. In the script, the story beats are laid out, which are the points of action which move the story along. There are also emotional beats which show what motivates the character to do things and reversal beats where new information is revealed where a character may decide to switch direction. There can be changes in pre-production and live-action movies sometimes have small updates to the script during filming, but it gets really expensive to change things once you get going.
For example, in the Disney animated film Frozen, Elsa was going to be evil and wasn't related to Anna. Then the songwriters began discussing what it would feel like to be Elsa, leaving out anything relating to being a villain. The song Let It Go resulted from that discussion, and that resulted in a complete re-write of the entire script to make Elsa and Anna sisters, with a different villain. Because of this, they lost several months of production.
Had this happened late in the process while the computer animation was under way, Disney would have looked at whether the additional expense of throwing away all of the previous animation was worth it. Movie studios don't like throwing away millions of dollars.
So once we see a movie or read a novel, the story has been finalized, the characters have been finalized and what kinds of antagonists and villains are in it have been finalized. Any changes that appear to happen in a character's role and importance are not because the story changed its mind. If at the end of the story a character is a secondary antagonist, they were always the secondary antagonist for that story. It's our perception of that character that changes.
Good stories use a variety of techniques to change our perception of characters. Plot twists, false protagonists and red herrings are just a few examples. They make the story interesting and enjoyable to watch or read. But they don't mean the story changed its mind.
Saying "Fred was the main, later secondary antagonist" is our opinion and perception of Fred's role in that story and are based on us thinking the story changed its mind.
Saying "Fred appeared to be the main antagonist but was later revealed to be the secondary antagonist" takes into account the entire story and what their role was at the end of the story.
When a character description is added to a page, write it to show the latter. Take into account how the character winds up at the end of the story, rather than saying it as if the story changed its mind.