Keep in mind the following before renumbering clients:

A client can be renumbered to any Client ID that is not currently in use. If you want to combine two clients into a single Client ID, use the Transfer A/R and Transactions program to combine billing and payment information.
The archived transactions will be renumbered as well. If your archive files are large, allow additional time for the renumber process.
If you use Tabs3 Billing Remote or a data capture device, you must merge all transactions from the remote workstation(s) before renumbering. Otherwise, entries using the old Client IDs will be rejected. After renumbering, be sure to recreate the Tabs3 Billing Remote validation files and transfer them to the remote workstation(s).
Clients renumbered in Tabs3 Billing will automatically be renumbered in PracticeMaster and Trust.
If the old Client ID is shown in the Pinned and/or Recent Matters lists on the Quick Launch pane, it will be replaced with the new Client ID for the user who performs the renumber process. The Client ID will be removed from the Pinned and Recent Matters lists for all other users.
If you are using the Client ID as part of the automatic document naming convention for PracticeMaster document management records, renumbering a client will not update the document name or move a document. You can run the Verify Documents program in PracticeMaster to update the file name and location.
Renumbering a client in Tabs3 Billing will renumber the Account Number in QuickBooks.
Renumbering a client in Tabs3 Billing will not update the Reference field for any associated GL Journal Entries.
If Tabs3 Pay® scheduled or recurring payments exist for a client, renumbering the client will cause the payments to be displayed in the Import Online Payments window as payments for an unknown client. When importing the payments, Tabs3 Billing will attempt to match them to the correct client based on the cardholder name and recent activity.
When configured for LexCharge® integration, renumbering a client will prevent any previous payment methods used for that client from appearing in the Credit Card Authorization window.
If PracticeMaster is installed and integrating with Worldox or NetDocuments, additional steps may need to be taken in those products after renumbering a client. See the Notes on Renumbering Clients topic in PracticeMaster Help for more information.