Bylaws are more difficult to amend than a policies and procedures manual, as bylaws usually require a larger majority for approval.
Policies and procedures manuals explain the “how” to implement the “what” that was identified in the bylaws. Any policies and procedures that are likely to change for practical reasons probably belong in the policies and procedures manual. Policy and procedure changes do not need to be reviewed by trustees as bylaws do.
Source: Document Library on staging.oa.org, under the category “Bylaws”: Bylaws and Policies and Procedures for Service Bodies