Not with RISA-3D. RISAFloor has this capability, but not RISA-3D.
In version 12 of RISA-3D, we are hoping to get RISA-3D to do live load reduction automatically. This feature would be based on RISAFloor information about tributary areas. Therefore, the feature would only be available for RISA-3D models which are tied into RISAFloor. At some point, it could probably be added to 3D only models. But, it will first be limited to only for Floor / 3D models.