Ctrl_Z will not work after running a macro, thus you have to rethink
Peo's comments.
Still, if you want a macro which will replace all formulas of a
selection to values, use this:

Sub FormulasToValues()
' Assumes the desired range has been selected first
Dim c as Range
For each c in Selection
c.FormulaR1C1 = c.Value
next c
End Sub

HTH
Kostis Vezerides