Presumably, most Starfleet designs are capable of it, even the Defiant-class.
What the hell would the Defiant-class have to separate from
? It's one discrete body, not different sections combined. Deliberately so, so as to make its various parts less vulnerable in battle.
does show that its nose-cone thingy is detachable as an emergency warhead, but that's not really the same thing.
That's from the DS9 Technical Manual
. The warhead is the last-ditch weapon to use when the ship is going down in flames, basically. So yeah, it's a bit of a stretch to call it a separable section; it's kind of the opposite of the usual lifeboat role of a separable saucer.