Since we’ve seen references to “Encounter at Farpoint,” in the TNG pilot, Riker and Troi are able to speak to each other telepathically.
That’s something a Changleing shouldn’t be able to duplicate (unless we’re going to go with the idea that their ability to duplicate organs and physiology would allow a Changeling to have telepathic/empathic abilities).
Honestly, one thing never broached in Deep Space Nine, is whether Betazoids would be a defense against Changeling infiltration. If a Betazoid is able to read Changelings (since TNG does establish there are some species that are immune to their abilities), they would be able to feel their deception and out an infiltrator.
Changelings alone shouldn't be able to do this, but it may be an easy task for Pah Wraiths living inside them
