Aviano Collection - 5 Piece Bathroom Hardware Accessories Set with 24" Towel Bar (Chrome Finish)

I only have room for a 17" or less towel bar. Is the bar itself attached to its brackets, or loose so can I cut it down to size?

What kind of tool am I supposed to use to remove the tiny screw? There's a round hole. No flat head or phillips head just a smooth round hole.

What is the diameter of the part that attaches to the wall?