Can we hide a Vlookup formula to enter new data in the same cell?

I have created a form in Google Sheets:

1. Row 5, Client, is a dropdown populated by existing clients.
2. Rows 6 to 9, Street Address, City, State, and Post Code, use VLOOKUP formulas to retrieve data from a separate sheet based on the Client
3. The Client dropdown is configured to "Show a warning" when invalid data is entered so that new clients can be added manually, as needed.
4. The image below shows sample data with a manually entered new client, "BurgertTory (Southbank)":
   1. The validation warning shows on the Client dropdown cell (arrow in image).
   2. The VLOOKUP functions in the address rows each return a #N/A error because they fail to match the client name.

Is there a way to create a toggle or checkbox so that the new client's address information can be entered in the address rows?