Close votes can be retracted from question, but after that no more close votes can be cast on that particular question.
I understand that voting and revoking several times would negatively impact queues and might could create a complicated situation; what I would like to have is to convert close vote.
I was in several times in situation voting to close a question as unclear, and after clarification it was off-topic for some other reason, e.g. not computer / product recommendation.
Also sometimes I'm just clicking too fast and select the wrong reason.
Having the possibility to convert already cast close votes would help to better indicate the reason of closure.