I can see how a borrowed neutral can be an unexpectedly energised neutral, but "become live"?how can you check that someone hasn't borrowed a neutral from your circuit to use for a light on a totally unrelated circuit that is currently turned off such that as soon as the relavent light switch is turned on your neutral becomes live?
Without some other fault? I don't see how.
Whether or not borrowed, or unexpectedly energised, Neutral is always a live conductor.