The foliage actor being locked vs movable or not has nothing to do with, well, pretty much anything.
You only have multiple foliage actors in world composition, and even then, only when you went in and set the foliage up into individual levels.
To place instances at set intervals, you’d have to create a batch system with world locations based on the level tile you are working in at the moment.
Its definitely possible. It’s not even that complicated as it can be done in blueprint… But it requires a bit of understanding on how the engine and foliage works.
Using the construction script on foliage also sounds like a bad idea.
Construction can trigger any time an instance is added/changed/removed.