Replacement Feats (3.5e Variant Rule)
From D&D Wiki
The Replacement Feat variant allows the PCs and NPCs to replace their feats automatically when they gain a class or template that duplicates EVERY part of the feat. For example if a Dread Necromancer takes the Tomb-tainted Soul feat at level 1, when he reaches level 20 he gains the Lich template which in effect makes the Tomb-tainted Soul feat useless. Under this variant he can select another Feat that would've been available to him at level 1.
Class features also do this, for example the Dread Necromancer's Undead Mastery class feature does everything the corpsecrafter feat does. The user may select another feat that he could have taken at the level on which he took corpsecrafter. In addition if a class or template can replace a feat, the class feature or template also may be used as a prerequisite in place of the feat, in the above example the Dread Necromancer may take any feat that has corpsecrafter as a requirement so long as he meets all other requirements as soon as he has undead mastery.