Option Explicit
Sub Bsp()
Dim str As String
str = "123.45.67.89"
Debug.Print str & " -> " & ReplaceRev(str, ".", ",")
End Sub
Function ReplaceRev(Expression As String, Find As String, Replace As String, Optional Start As Long = 1, Optional Compare As VbCompareMethod = vbBinaryCompare) As String
Dim s As Long
s = InStrRev(Expression, Find, , Compare)
If s > 0 Then
ReplaceRev = Left$(Expression, s - 1) & VBA.Replace(Expression, Find, Replace, s, 1, Compare)
Else
ReplaceRev = Expression
End If
End Function