If you are adding another find element inside (brackets) then you will need to account for that shift in the replace with value. For example:
.Text = "(" & arrA(i) & ") ([A-Z0-9]{1,})"
changing to
.Text = "(" & arrA(i) & ")([ \^s])([A-Z0-9]{1,})"
means that you also need to change the replace with to
.Replacement.Text = "\1 <<\3>>"

You can include extra parts of the number by including the stops in the wildcard search
.Text = "(" & arrA(i) & ")([ \^s])([A-Z0-9.]{1,})"

However you may find that if the phrase ends with a stop immediately after the number then it will also be included in the highlighted range.

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Andrew Lockton
Chrysalis Design, Melbourne Australia