Inspired by a bit of discussion over on discord, where there was an argument over whether the USS Discovery had been upgraded by the 32nd century Federation.
On the one hand, the Discovery did undergo a vast overhaul, being fitted with an upgraded power/propulsion system, detachable nacelles and the works, however, we also know at the end of Discovery Season 3, that Burnham resetting the Discovery’s computers effectively put much of the ship back to the 23rd century baseline (or as much of one as it could return to). We’re also shown that the Discovery still uses microtapes in its computer room.
So was the Discovery upgraded completely to 32nd century standards, or is it still a 23rd century ship underneath the 32nd century paint?
As you noted, it appears to be both, at least in terms of the computer systems.
Jett Reno noted that the warp plasma conduits were being replaced with polaric warp conduits, so I assume there was a total physical refit, albeit one thats very backwards compatible when it comes to archaic computer systems.