Here is a clearer link explaining the rules.
http://www.blessyouboys.com/2011/8/3...ined-hopefully"The position-player-for-position-player / pitcher-for-pitcher requirement is indeed now gone for substitutions prior to a series," O'Halloran wrote in an e-mail. "However, teams now are allowed to substitute for an injured player during a series. Such in-series substitutions are position-player-for-position-player / pitcher-for-pitcher, and the injured player cannot be active for the remainder of that series or the next series. Those substitutions also require MLB approval.