These instructions are for Word 2013 (or so) and LibreOffice 4.
For example create x with bar: x̅.
Select font Arial Unicode MS.
Type space, x, space and put the cursor to the right of the character x.
Word. Insert, Symbol, More Symbols. Font: Arial Unicode MS. Character code: 0305 (Combining Overline). From: Unicode (hex). Insert. Close.
LibreOffice. Insert, Special Character. Font: Arial Unicode MS. Click once the character Combining Overline (U+0305) (Subset: Combining Diacritical Marks). OK.
For example create p with hat: p̂.
Select font Arial Unicode MS.
Type space, p, space and put the cursor to the right of the character p.
Word. Insert, Symbol, More Symbols. Font: Arial Unicode MS. Character code: 0302 (Combining Circumflex Accent). From: Unicode (hex). Insert. Close.
LibreOffice. Insert, Special Character. Font: Arial Unicode MS. Click once the character Combining Circumflex Accent (U+0302) (Subset: Combining Diacritical Marks). OK.
Typing x-bar, y-bar, p-hat, q-hat, and all that! In Microsoft Word
Last modified: March 2nd, 2015
Author: Tomi Häsä (tomi.hasa@gmail.com)
URL: http://sites.google.com/site/tomihasa/combining-characters-with-unicode