Keuchel is 0-1 with a 4.96 ERA in six relief appearances, but Friday will mark his first start of 2013.
"I'm a starter at heart," Keuchel said. "If my role is in the bullpen, then it's in the bullpen. I'm going to try to pitch to the best of my ability. Friday is going to be no different."
He made 16 starts for the Astros last year and was 3-8 with a 5.27 ERA, including a complete-game win over Cleveland on June 23.
"One of the things you look at, the Rangers' lineup is left-handed dominant and they have some left-handed guys in their lineup, and we felt like if we can get both of our lefties matched up against them it would put us in good position," Porter said. "Dallas has done a tremendous job out of the bullpen and he's given us length every time he's come into the game, and we're going to give him an opportunity to get into the rotation."
Bedard made five starts before being moved to the bullpen and now finds himself back in the rotation. He's 0-2 with a 9.98 ERA as a starter this year, but in two relief appearances has allowed three hits and one run in 6 1/3 innings.
"The competition we have for these spots is a fluid situation, and it wasn't a competition that was going to end in Spring Training," Porter said. "I made that perfectly clear to the guys then. Obviously, moves like this kind of reiterate that to them and we're going to try to go with the hot hand and go with the guys that give us the best opportunity to win ballgames."
Humber got off to a nice start for Houston and had a 2.89 ERA in three starts, but he was 0-3 due to a lack of run support. He's 0-4 with a 16.20 ERA in four starts since.
"I talked to Humber and told him the same thing we told Bedard when we sent him down there," Porter said. "I said, 'It's going to be a situation you are built up and you've seen the long guys go down there and have success, like Keuchel, and end up back in the rotation.' Bedard went down to the bullpen and did a tremendous job last time out and he's going into the rotation. It's a fluid situation we will continue to monitor and this competition will continue to go on."
Bedard will pitch at Pittsburgh the following weekend, Porter said.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.