Is it legal to use the eagle from the Great Seal of the United States (as shown on the dollar bill) as part of a commercial design in a book? I am also changing the "e pluribus unum" to a slogan.
Use of the Great Seal of the United States is governed by Public Law 91-651, Title 18 of the United States Code. This is a criminal statute with penal provisions, prohibiting certain uses of the Great Seal that would convey or reasonably be calculated to convey a false impression of sponsorship or approval by the Government of the United States or any department, agency, or instrumentality thereof.
You can ultimately be fined and imprisoned for up to 6 months for use of the seal without written permission. You can read the details of the legislation here:
If your intended use can in any way be reasonably confused with an official endorsement or use by the Government of the United States then I would stay clear. Ultimately it is a decision you need to make but I would be careful either way and only use it if you can be certain it will not be confused as "Official".
Note: I am not a lawyer, this is not legal advice. If you require legal advice, contact a legal professional.