First Method:

1. Back up your data files.
2. Go to your Chart of Accounts.
3. Input the new Starting Balances (i.e. the tax basis amount) for each account on the right side of the screen under Account Properties in the Starting Balances column.

1. Back up your data files.
2. Access the Asset & Liability screen for the account to be adjusted.
3. Select the Balances command button.
4. Highlight the Starting Balance amount and change it to the tax basis amount.
5. Select OK command button.
6. Repeat for each account that needs to be adjusted.

As an option going forward:
After changing your starting balances to tax basis, you can prevent balances from being updated to market value in the future:

1. Select Investments | Investment & Account Options from the main FN menu bar.
2. Clear the Calculate Balances For box options.
3. Select OK.

Doing this will keep your account balances at tax basis throughout the year. You will still be able to update accounts to market value, however, the market value (and unrealized gains/losses) will only be reflected on your investment statements. All other statements will show the account balances at tax basis. So, if you want Balance Sheet reports to reflect market value, then do not change those settings.