What can be done to seat post too long/saddle too high?
I think what you are saying is that you need to drop the seat post all the way down into the frame, so the saddle is as close to the frame as possible. You need a seat post to connect the saddle and frame. You can't attach the saddle directly to the frame.

If the post cannot be slid all the way into the frame due to an obstruction it can be cut down to shorten it. As long as the minumum length is inserted into the frame you will be structurally safe. You can buy a shorter post of course.

However, if you need to drop the saddle all the way to the frame the bike is likely too large for you and possibly dangerous, as you will have no standover clearance.