Right know I am more of a mind to give invaders a custom_corpse, made of liquid:blood. I tested, anything that dies leaves it's equipment and a bloodsplatter instead of a corpse. I added a Crematory to burn vermin corpses, bodyparts and corpses, but corpses do not work, apparently hardcoded.
In my test game the invaders arrive with half up till full armor and no clothing. If I get rid of the corpses I have only goblinite left. On the other hand dumping corpses on something really hot would work as well. Instead of a reaction that takes corpses as ingredient I could just add a Junkburner to be build under a open space tile and use the ingame mechanic of heat to burn them. Would be a bit counter intuitive though.
Questions over questions... argh. I will continue for now to eliminate redundant features...
EDIT: DAMN IT. Completely forgot why I came here for the first place:
I know you can not edit/mod standart building, like adding reactions to them. Let's say burn wooden furniture to create coal in a wood burner- workshop. BUT can I not just delete the original Permitted_building:woodburner and add a new custom workshop, same name, same look, same hotkey, that has the Make ash and Make charoal reactions the original woodburner had, and then add more custom ones ?
If this works then you could in theory mod every building in the game...