The most common and most likely answer to this crossword clue is the 12 letter word MODIFICATION
M
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Buddy explains!

The straight part
We know that "change" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case change = modification.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MODIFICATION mean?
MODIFICATION noun- The form of existence belonging to a particular object, entity etc.; a mode of being.
- The change undergone by a word when used in a construction (for instance am => 'm in I'm)
- The result of modifying something; a new or changed form.
- The act of making a change to something while keeping its essential character intact; an alteration or adjustment.
- A change to an organism as a result of its environment that is not transmissable to offspring.
- A change to a word when it is borrowed by another language