Below is what I have. There are small pre drilled holes but I can add more or make the existing one larger. What is not shown in the picture is the fact that the legs are foldable. My plan is to build a table for which I should be able to quickly replace the top. The tops will be multipurpose: router table, a table with t-tracks and holes for bench dogs and a table for jigsaw like in the second picture
I would construct the table tops with an extra layer of 3/4" plywood or MDF on the bottom that is designed to just fit inside of the inner rectangular shape of the frame. This will align the top with the frame and keep it from sliding around on in a horizontal direction. With that in place the amount of hold down force that you need will be minimized.
One method to provide the hold down force would be to make some swivel blocks that are mounted on the bottom of the table. These would rotate on a single screw/lag bolt including a washer. The idea is that one end of these would be able to rotate to be under the edge of the table frame. You could cut the surface of the block that engages with the table frame at a slight taper so that the block tightens up as it is rotated.