Ah, so a similar thing has been done before. I guess with three hundred games (albeit "only" 110 bigs) a lot of ideas have been attempted already.
I suppose now that you say it, I can see how 2 votes once only would be fairly limited: if your preferred candidate was down by 1 and you'd already used 1 vote then you could only tie it up, not guarantee their death. With some strategy I'd expect it would change one lynch per game, but changing one lynch isn't necessarily a game changer unless you take a hit off an important role or move it onto one. Somewhat requires the user to have more information than the village.
I'd think giving them 3 votes once off would be more useful because then in tight races they can potentially bring in a whole new contender, without being a normal leaderlynch.
This is all just thinking aloud, though. I like Randakar ruling that a leader cannot save themselves.