If the refedit cell  has a formula  in than it must be the result of a
calculation of some sort dependent on other cells. It it the other
cells which must change to give the desired values in the refedit cell
so one or more of those other cells  must be changed, so perhaps you
could use Goal seek...

For n = TextBox1.Value to TextBox2.Value
Range(RefEdit).GoalSeek Goal:=n, changing Cell:=Range("C6")
Next n

You will have the value  you want in the refedit cell and the formula
will remain.


Note: C6 above is only an example cell address.