As title says, if you put passive point “Lone Guardian” midway leveling while you have limit of 2 skeleton warriors, your current skeleton wont be destroyed/removed (allowing to you have current maximum+1 skeleton warriors).
0.9d Acolyte (Summon Skeleton Passive: Lone Guardian does not affect existing skeletons)
This has always worked this way. Any changes made to minions must be respawned to see the changes in effect. If you respawn new skeletons they will have that limit in place.