Gah - a solution with more questions. – EntropicLqd
Legacy:BlockedPath
From Unreal Wiki, The Unreal Engine Documentation Site
The BlockedPath actor works by telling the AI of Pawns in the level that it is extremely inadvisable to set a course that leads through this point in the navigation network. This is done by setting an ExtraCost value of precisely 100,000,000 in the BlockedPath's properties. However, a BlockedPath can be unblocked simply by triggering it. While this is of no consequence to players, it is of much use to mappers who are trying to get good bot support into their levels, and is often used in Assault maps.
