The most common and most likely answer to this crossword clue is the 5 letter word FLUID
I've seen this crossword clue in The Daily Telegraph
F
L
U
I
D
Buddy explains!

The straight part
We know that "Likely to change" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case likely to change = fluid.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 FLUID mean?
FLUID noun- Any substance which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma.
- A liquid (as opposed to a solid or gas).
- (specifically, typically in the plural) Intravenous fluids.
- Of or relating to fluid.
- In a state of flux; subject to change.
- Moving smoothly, or giving the impression of a liquid in motion.
- (of an asset) Convertible into cash.
- Genderfluid.