Relabel legend values?

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How do I relabel a to ab

df = pd.DataFrame({"col1": [0, 1, 2, 3], "col2": [3, 4, 5, 6], "c": ["a", "a", "b", "b"]})
test = hv.Dataset(df).to.curve("col1", "col2").overlay()
test.redim.values(**{"a": "ab"})

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