A trial balance can be copied from one file to another. If you are copying a trial balance from an existing file, click to check Account Balances in the Clearing Components section on the next window. This will bring in a trial balance with all the existing account properties (including assigned map numbers) into the new file but without the account balances.
If you do decide to copy a trial balance from another file, be sure to then change the account numbers to agree with the client's account numbers, and delete any accounts which do not apply to that client. This will make it possible to import the client data (File > Import option). It will also allow you to print your adjusting entries and give them to the client to post on their accounting system.