Currently, the SNSSender can only reference existing attributes or user parameters (FME 2017.0 Build 17201). If the Subject and Message parameter values could be set with the Text Editor, it would be possible to create dynamic values, e.g. "Current Status is @Value(_status)!"
The current workaround is to use the AttributeManager to create an new attribute is this way, and then reference it in the SNSSender. It would great to have a one-stop-shop!