So, I am looking to create a method to take an extruded solid and give it a custom end profiling like the picture shows. I have tried manually adding vertices (splice) to the extruded shape but this just shifts the position of the vertices in the array and messes up the shape.
How would anyone else approach this problem?
Just adding vertices is not enough. You also have to ensure that the respective face definitions are valid. Are you working with Geometry or BufferGeometry right now? If you are working with BufferGeometry, is the geometry indexed or non-indexed?
Geometry, not BufferGeometry. Is there a way of redefining the face definitions automatically?
There is no existing function you can use. If you know the edges that are going to be connected to new vertices, you might be able to solve this issue. A half-edge data structure (sometimes called Doubly connected edge list) is very helpful in order to perform such topological operations.