Modifying Digit Fonts or Glyphs

I use Vedic Maths, and in vedic maths the normall digits 0 to 9 are used but 0 to 9 are also used with a bar directly across the top. I have tried macrons and overbars but these go between the digits; I believe it is possible to create ones own fonts,but this is an over-kill as I only need them over digits. Does anyone know of a way to use existing fonts and just create a duplicate of the 0 to 9 digits with bars over them?

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