So far, so very good!
I have finally made some progress, thanks to you, Willie.
Working so far:
Having the item equipped, and "activating" dead actor of "ABC" race, while also having items 1 & 2 in the inventory brings up a message whether I just want to loot it or to XYZ it.
Now I just need to somehow make an effect of: remove item 1 & 2, add item 3, mark as eaten.
I have decided to use HasBeenEaten anyway.
Sure, it will be impossible to do both cannibalism feeding and XYZ, but it is a good price to pay. Besides, my mod will focus on creatures. Still not sure if I want to add the NPCs to it.
Now.. back to work.