It seems that you can't do it from UI. However, from JSL, we can control the column display width. I am using JMP11 and not sure if GetDisplayWidth and SetDisplayWidth commands are in JMP10. See script below. The display width reduced from default 70 to 35.
//JSL
dt = New Table( "test", Add Rows( 1 ),
New Column( "Col1", Character,Formula( Repeat( "a", 100 ) )),
);
w=:Col1 << GetDisplayWidth;
:Col1 <<SetDisplayWidth(w/2);