"Have you stopped beating your wife, please answer only yes or no."
Would have to be no - now you prove I ever beat her to begin with.
c) avoiding the "perjury trap." Just as easily done by telling the truth - already addressed.
d) to avoid incriminating yourself? Which is what the fifth is for, to keep you from incriminating yourself in a crime that has already been committed. Which brings up the point I addressed earlier, are they a) admitting that they lied in the past, and don't believe they can sustain the lie in further sworn testimony, or b) admitting that they are incapable of telling the truth?
Doesn't look good either way.