If you are wanting to make invoice items from the Medicare list of items, you can use the 'Make Codes' function in Setup > Financial > Charges > Invoice Items.
This option only 'makes' new items it does not amend or remove existing invoice codes.
The Incisive will respond quicker to to invoice lookup requests if there are fewer items in the list. It is better to limit the invoice items to the range that are relevant to your sub-specialty rather than importing all the Medicare items.
Unwanted invoice items created from the Medicare list cannot be removed in a bulk lot.
In a specialist centre, if each specialist manages their own invoice codes, their secretary can import their own range of (sub-specialty) items without affecting other practices.
The 'Make Codes' function does not amend nor remove existing invoice codes.
A short video tutorial (2.04 mins) demonstrates the steps involved with adding new invoice items from the Medicare list
http://incisivesupport.com/train/vid/Invoice_MakeItemsFromMedicare.mp4
Further information is available in the online Help.