You don't need to split the found string when it is just one number
Code:
Sub FindTemplate()
Dim aRng As Range, str As String, int1 As Integer, int2 As Integer, arrStr() As String
Set aRng = ActiveDocument.Range
With aRng.Find
.ClearFormatting
.MatchWildcards = True
.Text = " [0-9]{2,3}"
Do While .Execute = True
int1 = CInt(Trim(aRng.Text)) + 2
aRng.Text = " " & int1
aRng.Collapse Direction:=wdCollapseEnd
aRng.End = ActiveDocument.Range.End
Loop
End With
End Sub