This is not the best practice, if he create or destroy anything in the meantime, he will bug his game.
"IIDs and UIDs in the editor don't change depending on the Z order, but they do change if you delete and insert instances. Because of this you should not rely on knowing UIDs or IIDs in advance at all - the instance with UID 3, for example, could change to a different object if you add or delete some things in the layout view. This could easily break your game or make it work differently "randomly" (it will seem random to many users because they won't realise certain things they did changed the UIDs and IIDs). For this reason I don't think UIDs or IIDs should ever be displayed in the editor, in order to discourage this bad practice."