Nah, doing that will actually make your ballot less useful in cases where you approve of both the candidates that made it to a runoff round, because you ranked them both the same, and thus your ballot can't count as a "vote" for either since you indicated no preference.

For single winner this is will probably be a rare issue but for multiwinner, which is what I want, that could end up biting you as the margins close in for the last seat