Startup Costs

IRS Publication 535 states:

Note

The election to either amortize or capitalize startup or organizational costs is irrevocable and applies to all startup and organizational costs that are related to the trade or business.

You may file a revised statement.  See here.

Revised statement

You can file a revised statement to include any startup costs not included in your original statement. However, you can't include on the revised statement any cost you previously treated on your return as a cost other than a startup cost. You can file the revised statement with a return filed after the return on which you elected to amortize your startup costs.

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