Hi I think I haven't updated myself much on the subject , but is still not possible to add and replace an animation just for some npcs only for example during an idle but not alter the same one for other npcs?

Like to be more clear , make some hold a spear in a certain way and leave all rest do it the way is done vanilla?

It's possible but I don't remember how. There was a "Run like a khajiit in sneak" mod that explained how to do it on the Nexus.