No it doesn't, and when the constitution is silent on something that's where individual opinion and interpretation comes into play. This is particularly true when CdeC is supposed to determine if a candidate "contributions" are adequate to become a citizen, neither contribution nor adequate are defined leaving it open to interpretation.The Constitution doesn't say anything about making previous contributions either, so it's safe to say that neither of our positions are based on it.
That's your opinion and you're entitled to it, however using your example of Ferrets this statement doesn't even agree with your what your actions would be. His behaviour is terrible, always has been always will be, his contributions of real value are next to non-existant, and yet just because he had citizenship before you want to give it back to him. He didn't deserve it in the first place and his actions since before then and certainly since afterwards have proven that again and again and again.I don't think the contributions are nullified and so the only thing would stop a removed citizen from being readmitted, in my books, is whether the behaviour is adequate.