Due to the signing of Form 8332, Bernice has no recourse for 2010. She can avoid the five-year restriction by revoking the prior waiver with the filing of another Form 8332. Unfortunately, this is effective beginning with the year following the filing (i.e., 2011 in this case). She must also provide written notice of the revocation to Nate. This can be done by sending him a copy of the new Form 8332 she has filed.
Presuming Bernice escapes the commitment she made on the original Form 8332 for the next four years, is she bound by the divorce decree? Not according to recently issued Reg. § 1.152-4 interpreting Code § 152(e). State law (including divorce proceedings) does not control how dependency exemptions are allocated for Federal income tax purposes. Under § 152(e), the exemption(s) belong to the custodial parent unless that person issues a release. For divorces on or before July 2, 2008, a decree could serve as a release if it provided the same information as contained in Form 8332. The new Regulations, however, even allow such implied releases to be revoked by the custodial parent.