A system provides for the remote activation and deactivation of a downhole tool such as an agitator tool. The downhole tool uses a dart-catching section configured with a profile that engages with a corresponding key section of a dart. Different tools in the string may have different profiles, allowing darts to pass through tools to reach a tool with a matching profile further downhole. The dart includes a removable nozzle that can be detached by a object dropped from the surface, after which a second dart may be dropped to engage with the first dart to change operating parameters of the tool.