Currently, the FX menu allows you to delete or insert certain effect. If you wish to replace an effect with another (for example, a delay by another delay), this requires at least two operations (delete an old/add a new fx or add a new/delete an old fx). To improve workflow, I suggest creating an option to simply replace the fx (what would require only one operation).
Additionally, it could be created a "Replace FX Chain" option.
Regards,