Since Millénaire 2.7.7, changes to Millénaire can be done via the "mods" folder. Any folder inside is considered a mod by Millénaire and can contain all of the Millénaire types of files  (buildings, villages, villagers, translations ...): just organize it like the content of "millenaire". The "mod" "examplemod" shows how to override a file (crops/normal/lonebuildings/abandonedmill.txt in this case) and how to add a new goal, a new quest, a new block and a new object.

The old folders "millenaire-custom/cultures", "millenaire-custom/custom cultures" and "millenaire-custom/quests" should no longer be used and will be removed in a future release. I leave them only so as not to break the custom content created under the old system.