Yes!
Basically, yes. (But then, that's what you'd be doing with a "Null" vote anyway. This way is clearer about that.)
Yes, and this is a part of why I'm trying this rule out. I have observed the vote tracker sometimes get slightly off because of having what it thinks is multiple votes in the same post. In this case, just vote to lynch the other player and your previous vote will be overwritten, both in the vote tracker and in the rules.