Currently when I need to add a new input I copy all of the components from a cluster, paste outside, and then make a new one. Is there a way to add or remove an input to a cluster without having to make a whole new one?
Yes, just add a new Cluster Input inside the cluster.
Unfortunately, renaming cluster inputs and outputs doesn’t work. The work around is to add new inputs and/or outputs, save changes, move the external wires from the old to the new, then re-edit the cluster to remove the old (now unused) inputs and/or outputs.