Manually assigning a line number on an order

Does Oracle have a best practice on manually updating a line number on an order when its created?  Example, We want to be able to associate a particular fee or charge to a Stock line the may or may not include other products.  We would add the associate fee and manually change the line number to be XXX.001.  This allows us to link the associated fee to the particular part that we also want to change our customer for.  See below...

   

Line Number	Part Number	Description
1.000	10	Blue Bike
1.010	123456	Installation Fee

This will allow us to Invoice the Custom for both the Fee and Product at the same time because we have a custom speed status update program to advance the lines to an invoice status.  We would like to know if there are any standard around a particular process like this.  Any help will be grateful, thanks!