Hard drive located and game, and more importantly editor(though the shortcut didn't get on the desktop automatically), successfully reinstalled. Better than it was before the OS change because the minimap and file tree parts of the editor UI weren't functional previously, as it was the Windows version being run on Linux through a semi-emulator... thing. Having quickly checked, corpses and trees both seem to be hardcoded variables that aren't valid for units "properly" (could just be a facet of the automatic cast), so fractal corpses are off the table, but generating Neutral Passive units when a corpse is used has to be good for something (meatsacks for HP stealing, maybe?). Similarly, the ability must be on both units and have the desired fields applied to the right units. If you don't set it properly, it "loops", having the unit turn into another of itself.
However, said rapid initial testing shows the following behaviors on the ability this thread is about:
Build abilities are retained: Having the alternate unit set to an Acolyte (I freaked out and refused to finish the test when set to Peasants because all of them morphed into Paladins) and original unit set to Paladin had the Paladin keep the build ability from the Acolyte. Unsummon, Sacrifice and Gather were not. When I added a built structure (Scout Tower), it would not build properly for the former Acolyte trying to built a Scout Tower, not even initializing construction. It also didn't work properly for the one who wasn't, but that was due to lacking the repair ability. Upon adding a ziggurat to the list, it initialized under Human construction rules (repair to build) for the non-former-acolyte and under Undead summoning rules for the former Acolyte. This is the general pattern, using the construction method of the previous form, with a former acolyte Wisp not being able to build anything but the Ziggurat added to the list. This means that you can, as an example, have the Orc build method attached to what would normally be the Night Elf build method, getting a reusable worker in a non-reusable race.
"Egg" Units Time to become "Original" units: As mentioned above, the five Peasants I started with (because rapid test map) turned into Paladins when the timer ran out. That's... That's all I need to say (no, seriously I freaked out)
Heroes do not function properly: They become a different iteration of the same Hero, with ability score effects stacking, but the scores themselves not stacking. This is a severe problem because the abilities learned aren't carried over, if they were, you could use it to replicate the Tarrasque from Starcraft (comes back from death, stronger each time) on a Hero. I mean, you can still use it that way, but not for a conventional Hero with actual Hero abilities. Maybe if you intend to have a tradeoff for survival versus revival, or used triggers to store learned abilities and use triggers to re-learn the appropriate abilities, but at that point you might as well replicate the ability with triggers outright. Alters don't work, meaning triggers have to be used to revive (maybe triggers can restore alter function by properly removing them on unit death?). However, usefully, the effects of the ability scores carry over to non-Hero "egg" units and items are only dropped if the unit lacks the appropriate inventory space.