I can't seem to find a way to replace one title ( A ) with another (B/which is a copy of A with a different text)
In Legacy title the command is simply option/drag and drop onto the graphic in the timeline... which will also replace the name of the clip in the timeline to whatever I named that copy in the project bin.
Essential Graphics don't live in rhe bins, only the timeline. They're named after the topmost layer in the stack inside the graphic. Just delete the old graphic and drag the new one to the same spot, no need to option-drag.