What I meant is that the ultimate delivery of a photon torpedo is an energy weapon, even if the hard casing remains intact until impact.
Exactly. Leaving the tube and becoming a glowing ball of light does not yet mark a transition from "casing" to "energy"; that apparently only happens at impact.
However, the warhead within can apparently be swapped with relative ease - we have seen these casings loaded with sensors or even live people at times, and supposedly the newfangled "quantum" warheads go into the same casing (since the Defiant has these standard casings aboard).
So if you want a kinetic effect at the target, just install a lump of lead. Or of some superdense material kept stable by treknomagic. Or a gravitic device that gives the torpedo the momentum of an object a thousand times heavier.
We also occasionally learn of our heroes packing various exotic warheads or demolition devices, such as tricobalt weapons or chemical explosives. Phasers and photon torpedoes seem to do the trick in most cases, though.
That would make sense to me. Pack a photon torpedo casing with a warhead and you're all set for some good old fashioned explosive action.
Too bad we never saw an episode where they explicitly did this, meaning a direct reference to reconfigure a photon torpedo shell to carry a thermonuclear device.