Jumping in a little late here, but I think the intent was that "unplanned" redispatch = change destination enroute (distinct from diverting to an alternate). The way I interpret it, diverting is proceeding to the listed alternate or another legal airport (destination mins + other various airport suitability regulatory requirements) when the intent was to land at the original destination and conditions outside the company's control prevented it. This could be a weather diversion, closed runways, etc. Usually a decision to divert would occur in relatively close proximity to the intended destination. A new alternate would not be required.
On the other hand, I would refer to a destination change as a redispatch because 121.631f requires several FARs to be met "at the time of redispatch" when changing an original destination enroute. I fully understand planned B044 redispatch/planned rerelease. However, I think the word planned is purposely included in the OpSpec. A flight can only be dispatched to one destination on a flight plan. Therefore, the flight must be redispatched if the destination is changed IAW 121.631f. I find this to be distinct from a diversion, since diversions occur when conditions outside the company's control prevent landing at the flight plan destination. If, for example, the company decided (enroute) to go to MSP instead of the originally planned destination on an ORD-SEA reposition flight, then a change of destination has occurred and 121.631f applies, including the requirement to designate an alternate (maybe the dispatcher lists RST along with the destination change to MSP). All that said, I would consider that scenario to be redispatching the flight, since the destination has changed in a non-diversion scenario and the flight must have a new dispatch release to MSP.