Sure, that's what I normally do, but I was a bit short on time yesterday.
How do you see it happen/work?
The way I see it now, is that you have your invoice numbers in column B. The mentioned invoice number is in B2. The code below will ask you how many invoice numbers need to be created.
Dim qAmount, rPart, x, y As Integer
Dim lPart As String
qAmount = InputBox("How many invoice numbers would you like to create?")
lPart = Left(Range("B2").Value, Len(Range("B2").Value) - 3)
rPart = Right(Range("B2").Value, 3)
For x = 3 To qAmount + 2
y = y + 1
Range("B" & x).Value = lPart & rPart + y
Let us know what you like to see different.