Sorry, I should have elaborated a bit more. Your theory, to the extent I've been able to test it, was perfectly sound: buildings that don't build units caused a CTD everytime I tried to make them a condition for another unit (that applies to buildings that recruited units in vanilla, but from which I had removed that capability). Conversely, buildings that build units can be made prerrequisites for units built somewhere else. And that is valid for buildings that did not even exist in vanilla. I implemented a completely new building, made it capable of recruiting peasants and worked perfectly well as a requirement for units recruited at the barracks. I would guess that it also should work with pre-existing buildings to which you add the recruiting capability.

HOWEVER, the above simply does not seem to apply to core_buildings. Units recruited there simply won't admit any building in their requirements, regardless of whether it recruits units or not. In my experience, this is valid for both units recruited at core buildings in vanilla or units made recruitable there in a modification.

Again, thanks, Pode. I am finally progressing in things I wanted to implement.

A.