You need to put a conditional script in the "Text Appears When" section of the dialog editor for that conversation node. For example, a local variable on the player that the script checks for. This way, the "uh oh" line only shows up if the player has been flagged as having visited the wizard's home. To change the order of the nodes in a conversation, highlight the node and hold shift+left click to drag it to another parent node in the conversation.
