Tool layers have all the same behavior as group layers—you can add, remove, rename, and reorder sublayers. Because the sublayers of a tool layer are created (or re-created) every time you execute the tool, there are certain behaviors you should be aware of.
Renaming a sublayer
When a tool layer is executed (right-click the layer and click Open), it creates or updates sublayers based on the names of the tool's parameters. If you rename a sublayer that is the output of a tool, the next time the tool executes, a new sublayer will be added and the renamed sublayer will remain. For example, the output parameter of Buffer is Output Feature Class. Changing the name Output Feature Class to Buffer Results, then executing the tool layer again, will result in two sublayers, Buffer Results (the old results) and Output Feature Class (the new results).
Deleting a sublayer
If you delete a sublayer that is the output of the tool, it will be re-created the next time you execute the tool.
Adding a sublayer
You can add a new layer to a tool layer, just as you can for a group layer.
The only issue with adding a sublayer to a tool layer is that it can lead to confusion—two tool layers based on the same tool have different sublayers.
You can change the symbology of any sublayer by right-clicking and clicking Properties. Symbology of a tool sublayer will be maintained between executions of the tool layer as long as you don't change the value of the output parameter on which the sublayer is based.