There are two positions in the script which are important in this case. One if the hotkey assignment scene and the other is the hotkey use during the map scene. The methods are "class Scene_Controls" in part 3 line 7090 and "update_skill" in part 3 line 3848 with "update_item" in part 3 line 3894. For the first part: Somebody would need to edit the scene a bit so only 3 keys are assigned and that your HUD add-on is used for it instead. For the second part: Instead of iterating just through the numbers for the hotkeys, they should iterate through the numbers but use letters for the activation.