He said the changes weren't a big deal.
"We're just trying to get guys that might be able to do something a little higher up to get more at-bats," Mills said.
Lee had not hit third since May 7, 2010. He only had 39 at-bats in the third slot in the lineup during his six seasons with the Astros, all coming in 2010.
Mills said he talked to Lee two weeks ago about the move. He also emphasized that the move wasn't all that important, considering Lee is still batting behind Jed Lowrie and in front of Brian Bogusevic like he has many times this season.
"To make a whole lot of noise about the numbers, I'm not sure if that's the right thing to do," Mills said.
Lee went 2-for-4 with two doubles on Saturday, picking up two RBIs.
The last time Schafer batted eighth was May 22 against the Cubs. On Saturday, he broke out of an 0-for-14 slump with a solo home run in the sixth. He went 1-for-3.
Mills said he and hitting coach Mike Barnett stayed late on Friday night to talk about how the Astros can bust out of their hitting slump. The team responded with eight runs in Saturday's victory.