Hey Davision,
You are still able to create a BP from a collection of placed objects in your scene, the process is just a little different. If you have a static mesh in your scene and you wish to add components and other meshes, simply use the ‘Add Component’ dropdown menu in the ‘Details’ tab of your selected mesh.
Static Mesh Actor Blueprint
Here I used the add components button to add the Static Mesh actors to the original mesh. Since I am doing this within the perspective viewport, I have greater control over snapping and placement of objects.
Added Components
This is what the ‘prefab’ or blueprint looks like pieced together in my scene. After you have all your objects placed how you would like, use the blue button ‘Blueprint/Add Script’ which will prompt you to name the blueprint you wish to create.
Let me know if this worked for you as a solution, or if you need further assistance or have any other questions.
Thank you,