Can a Letter of Wishes contradict my will or trust?

No. The Letter must align with the formal legal documents. Kris Kluver, in The Dysfunctional Family Office, makes this point directly. Even though the Letter is non-binding, its content cannot contradict the established structures and legal documents associated with the wealth transfer. If the Letter says one thing and the trust says another, the Letter creates ambiguity that produces family conflict during one of the worst possible moments to have it. The fix is to draft the Letter and the legal documents in parallel, with both teams aware of each other's work. The Letter expresses intent in plain language. The legal documents implement that intent in enforceable form. They should read as the same direction in two different registers. Most founders draft the legal documents with their attorney and never write the Letter. The result is a legally airtight plan with no human context.