Well, you should be able to replace this....

Master!$R$3,A2

with this...

Master!$R$3

to do what you want.

That won't work though, because in the next row it is A3,
then A4 and so on until A1000

There is always the macro world...

Sub RemoveAx()
Dim R As Range
Dim SecondComma As Long
For Each R In Range("A1:A1000")
SecondComma = InStr(1 + InStr(R.Formula, ","), R.Formula, ",")
R.Formula = Replace(R.Formula, Left$(R.Formula, _
SecondComma), "=CONCATENATE(Master!$R$2,")
Next
End Sub

Rick