There are two ways:
1. You can do it manually by unticking Enabled in the Attributes Manager for the Range Mapper under Basic tab.
2. You can control it via Xpresso (or User Data) as well. To control by Xpresso, add a Range Mapper as you normally would, You then need to drag and drop the Range Mapper icon from the Attributes Panel to the Xpresso Panel so you now have what looks like two Range Mappers. On the new Range Mapper, you now have an Input (Blue Side) of Enabled which you can trigger any way you like, but as my example, with a Boole Node. This changes the original Range Mapper, so you can activate/deactivate Enabled as required. Note that you need to keep both Range Mappers, the second one is only used for Enabling/Disabling the first Range Mapper.