Your profile indicates you are using TurboTax Business (at least your post is tagged that way) and, as far as I have been able to determine, TaxSlayer does not offer a product that can produce an income tax return for a business entity (e.g., corporation, partnership, estate/trust, etc.).
Regardless, you can override virtually all of the lines in almost any form in Forms Mode, but doing so generally precludes you from e-filing your return (i.e., you need to print and mail the return).
If you could provide more details concerning exactly what you are trying to accomplish, however, that would be extremely useful.
