Change rope with top sliced off (5)

I believe the answer is:

alter

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'change' is the definition.
(I know that change can be written as alter)

I can't explain the rest of the clue.

(Other definitions for alter that I've seen before include "Metamorphose" , "and 10 Across: Second self" , "convert" , "Make changes to" , "Change, maybe later" .)

I've seen this clue in The Times.

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