[Haskell-cafe] How can i safely change the value of specified key ?

[zaxis]

aaa <- newIORef ([]::[(Int,Int)])
writeIORef aaa [(1,1),(2,2),(3,3)] 

then if i want to change aaa to [(1,1),(2,222),(3,3)] , what's the best way
? 
re-write aaa is not permitted.

Sincerely!
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