Add New Line Item Detail to Invoice Based on Status

[breakingme10]

I'm doing my storage unit database and going through and trying to figure out how to get the invoices that are marked as "late" to add another "product" to the invoice called "late fee" which is already in my products table. i just need to find the right method of automatically adding that to the invoices marked late. can anyone help me with this? i can post an empty version of my db if you need me to. but the client data is very sensitive so i can only give you a blank sample db to see what i've already done.

EDIT: db too big to upload here, i uploaded it to google drive

https://drive.google.com/file/d/0B9J...it?usp=sharing

[breakingme10]

So i've tried VBA

With Me.[sfrm_InvoiceDetails].Form.RecordsetClone
.AddNew
!Item=32
.Update
EndWith

but it gives me the error "a related record is required in tbl_Invoices", but i'm adding an extra line to the details subform so the InvoiceID field isn't populating with the CurrentRecords invoice#. That is my hypothesis anyway. How to I get it to add that records invoice#?
Add a line under !Item=32 like !InvoiceID=CurrentRecord or what? I suck at VBA i'm sorry. Please someone help me on this?

[breakingme10]

Update: i got it working but now it adds the late fee everytime the form is opened and it sees that the status is overdue. how can i make it check to see if the late fee is already in the item list before adding it.