Not all data can be changed. Some values are for Read Only.
To know what cheat code does, just hover mouse on the checkbox or other item and wait for 1 second and explanation will pop up.
Tab "Limits"
To change Enemy Skills in materia: put E.Skill materia in the inventory in slot 1, then click on the Refresh button or click on the empty spot outside of GroupBoxes, and change Enemy Skills in materia with checkboxes.
Tab "Cheats" :
"Remove All Materia" and "Remove All Items" buttons, removes all materia or all items from inventory.
Tab "In-B Enemy" (In-Battle Enemy):
Values from AP and below are for Read Only.
Tab "In-B Status" (In-Battle Status):
To disable Cait Sith's Limit Evil flag: click on the checkbox "Evil flag enabled", after first reel is stopped. Checkbox must be Unchecked to disable Evil flag.
Tab "Coord" (Coordinates):
To track location of the Ultimate weapon: When Ultimate weapon is flying somewhere on the world map, click on the checkbox "track the location of the Ultimate weapon". Where on the World map: "H" is Highwind or Cloud, and "X" is the Ultimate weapon.
Also right click on the GroupBox "Field Coord", the same options as in the menu items will pop up. See screenshot with Coord Tab.