I thought it was able some time ago, but currently I can add spline components, but can’t edit them directly in blueprint viewport. Is it a bug?
Just checked this for you in 4.12.3 and I was able to edit the spline in the game viewport but not the blueprint viewport. I believe this was removed a long time ago. I am checking whether this is something we plan to implement or if it’s missing by design.
Turns out this feature (editing splines in blueprint viewport) is coming to the engine soon. Current expected release is 4.13.