You simply check all the entities wanted ( can be done faster by selecting all with the ''select:'' option), then you select the action ''rename'', put the name you want and check Multi Name . Then, all the selected entities will have the same name given with a number associated.
There was an option to select all in inventory, up to a maximum of 1500. However that has disappeared at some point, and will likely be brought back when the coders have time for it.