The Changeling race in D&D 3.5 has a history defined as
They evolved through the union of doppelgangers and humans, eventually becoming a separate race distinct from either ancestral tree.
In D&D 3.5, there is also a list of Changeling Racial Feats, including but not limited to Racial Emulation:
Racial Emulation (Races of Eberron, p. 110)
You can emulate a humanoid more closely with your minor change shape ability.
Now, can a player character with the Doppelganger race take any of those feats, Racial Emulation in particular?
RaW, I'd say probably not, but seeing as how the player is choosing a LA +4 race for the superior version of Change Shape and continuous Detect Thoughts, I'd be inclined to allow it - since we're talking about feat(s) to support an ability the Doppelganger has a better version of than Changelings.
Thoughts on balance? Would house-ruling to allow this wreak havoc with game balance? Is there something in the rules that would actually make this legal without needing house-rules?