The OP referred to adding an overbar or macron to the letter x. When I type
x and then 0305 as you suggested, I have x0305 with my cursor after the 5. In
this case when I press Alt+X, nothing happens. If I insert a space after the
x, Alt+X does convert the number into an overbar, but the two characters do
not align properly even when I remove the space between them.