Not sure what you want but try replacing with:
Code:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim cll As Range
Set cellsToProcess = Intersect(Target, Range("B2:J4"))
If Not cellsToProcess Is Nothing Then
For Each cll In cellsToProcess.Cells
With cll.Validation
If HasValidation(cll) Then
If .Type = xlValidateInputOnly Then
If Len(cll.Value) > 0 Then
cll.Select
.InputMessage = InputBox("Confirm/Edit customer ID for selected cell", , .InputMessage)
.ShowInput = True
If .InputMessage = "" Then .Delete
Else
.ShowInput = False
End If
End If
Else
If Len(cll.Value) > 0 Then
.Add Type:=xlValidateInputOnly
cll.Select
.InputMessage = InputBox("Enter customer ID for selected cell")
If .InputMessage = "" Then .Delete
End If
End If
End With
Next cll
End If
End Sub