Paste a representative sample of your data into a post so's we can have a look.

Gord Dibben  MS Excel MVP

If I understand you correctly, you would want the string:

ab12ab33

to change to:

ab(1)(2)ab(3)(3)

This UDF will do that.

To enter the UDF, <alt-F11> opens the VBEditor.  Ensure your project is
highlighted in the Project Explorer window, then Insert/Module and paste the
code below into the window that opens.

To use this function, enter a formula of the type:

=parennums(A1)

If you want different functionality, it's pretty easy to change this.  Post
back.

================================
Option Explicit
Function ParenNums(str As String) As String
Dim re As Object
   Set re = CreateObject("vbscript.regexp")
       re.Global = True
       re.Pattern = "(\d)"
ParenNums = re.Replace(str, "($1)")

End Function
==============================================
--ron