But he's made an exception for Yasmani Grandal, who has seen positive results in July after adopting more of an upright stance last month to alleviate discomfort in his surgically repaired right knee.
"We worked a ton, changing my whole batting stance and trying to get in a good spot so the knee doesn't get any stress on it," Grandal said. "Just standing up a little bit more, making sure my foot is down in a good spot and trying to stay on my back leg a little bit more. Usually those are things you do in the offseason, but we had to make the changes for health reasons."
The switch-hitting catcher was batting .293/.383/.488 in 12 July contests entering Sunday with two home runs, including a mammoth 440-foot moonshot on Saturday, the longest homer hit at Petco Park this season. It's a small sample size, but those numbers are nearly identical to the .297/.394/.469 line Grandal put up in his promising rookie campaign, when he posted a 2.7 WAR despite playing just 60 games.
Even though Grandal has been in the Majors since 2012, he hasn't accumulated 500 at-bats in his career due to injuries and a suspension for testosterone use that caused him to miss 50 games last season. So three seasons into his big league career, the Padres still don't know for sure what they have in Grandal.
Do they have a switch-hitter with power who can be their catcher of the future? Or will his balky knee and struggles from the right side, where he's hitting just .125 with 11 strikeouts in 32 at-bats entering Sunday, derail his potential?
"You never know when [the pain] is gonna come back," Grandal said. "You just take the new stance and make it your own."
His power stroke hasn't disappeared over the past couple of years -- in 2012 he clubbed eight homers in 192 at-bats, and this season he has eight homers in 202 at-bats. But he needs to hit for average, too -- he's batting at a .213 clip entering Sunday despite his recent surge.
Regardless, Grandal's overarching goal for 2014 is still within reach.
"The first day of Spring Training I said I wanted to be healthy throughout the season," Grandal said. "So far, so good."
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. Will Laws is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.