This excerpt taken from the PBI 10-K filed Mar 13, 2006.
Changes to Participation Agreement. Provisions of a Participation Agreement pertaining to the amount and source (e.g. salary, specific award, etc.) of Deferred Amounts may not be amended or revoked after the beginning of the Plan Year to which they pertain. Changes to the In-Service Distribution Dates, and Form of Payment elections for In-Service Distributions and Retirement distributions may be made in accordance with provisions in applicable Sections of the Plan.