Simply said, I want to add a mesh component to a spline, but have this mesh be determined by whoever is using the blueprint the level editor, rather than have to go into the blueprint construction script- find the node- replace it there and recompile the blueprint.
Is that possible?
Currently I am stuck at actually providing it the input to the node since it wants an actor instead of the mesh?
You can do it with a Static Mesh (asset), as above. But not with an Instanced Static Mesh Component.
I think by ‘mesh instance’, the OP means ‘a mesh’ ( as you probably guessed ) 
I meant this, OP is feeding a component into a component:
If we’re using ISMs, perhaps that’s what was needed:
Ah yes, see what you mean…
Got a call from work so I couldn’t answer any sooner, but yes that Is what I was trying to do, because from my limited understanding I assumed that using instances would be more efficient?
Since its essentially creating a new mesh along the spline. Unless it boils down to the same thing?
Essentially, instead of setting the Mesh inside the node details, I want to provide it through a parameter.
But I think what @ClockworkOcean posted above may be what I was looking for by giving the target to a set static mesh node?
Yes that was indeed what I needed to do, good to know I can do that, I was too focused on how to provide the input directly to the Spline Mesh Component node.
Note the word component - it’s a like a module we add to an actor:
Static MeshStatic Mesh to create many highly performing instances - think of them clonesStatic Mesh and applies tangents and whatnots to deform itStatic Mesh is the asset you import into the engine for other components to use.
In short: Components use Static Meshes to do their special things. A component cannot use another component for that.
If an actor is a chest of drawers, components are drawers and static meshes are the contents. You can’t put a drawer into another drawer. May be a stupid example but that’s the first thing that came to mind 
Got it does make sense, no worries about the example 