to me that the alteration comes from someone trying to make sense of bare face and turning it into bold face to do so. Interesting isn't it?
It goes from "bald-faced" to "bold-faced". That's how eggcorns work--if the origin of a word isn't obvious, people will adapt it to a similar word that is more frequently used, and that sounds like it makes sense.
For example, many people write (and say)
per se as
per say, because they think
per se means "so to say".
Similarly, "for all intensive purposes", because people use the word "intensive" fairly often, and the meaning of "for all intents and purposes" isn't obvious.
So someone hears "bald-faced liar" and then misremembers it as "bold-faced liar" because a) bald-faced liars are bold, and b) "bold-face" is a more commonly used word than "bald-faced".