Make sure stair units do not slide, ramps and rakes are not too steep, steps are not too high, platforms are not wobbly. Listen to the actors requests and complaints and respond to them to provide a safe set. The same guidelines as backstage apply for these spaces. There must be an illuminated path for the actor to get to the playing space and exit from it. If an actor is playing a scene in the grid you must remove anything loose and sitting in the grid or on the airducts that can be knocked off.
Actors can climb down from the grid to the stage via ladders.
You must tell me about these plans well in advance and I will require the director and actor to prove to me the safety of the device and the action. Actors can be hoisted up a few feet or suspended for short periods of time. Any plan to do this requires advanced notice to me and use of special rigging and harnesses that I can provide. The director, actor and crew will have to prove to me that they can safely accomplish the effect. Yes you can screw into the floor of the ex, just try not to go nuts with it.