When you use Multi Assign, it should have an Option that you can check to choose to automatically remove other Appointments and reassign to new Resource/Technician plus a setting to configured this as a default in Service Board and a user Setting where they can choose another method. Plus an option check a 'Remember this preference' similar to Dispatch Console.
What is the underlying problem do you intend to solve with this idea?
Easily reassign a job without dragging and dropping to a huge list of resources
How is the problem being addressed today, if at all?