Yamaha turntable YP-211 question

Probably sound better that way. Better still, experiment with wood blocks and other materials like dive weights or lead shot in a bag. BDR Cones will beat all especially if the table has 1/4-20 threads to screw them into. Nothing responds better to vibration control than a turntable.

I'm sure the sound would be changed if the bottom cover was in place , it also is where the feet mount. I would get a piece of pressed wood or even plywood and replace.

That is fine!