Legal Question in Wills and Trusts in California

Yes, but only if a Judge approves the changes.

Wills are not irrevocable until the testator dies.

I agree with Ms. Cusack and disagree with Mr. Jordan. An irrevocable "trust" is modified by a petition filed with the court and the judge's approval. A will is different. A will is not irrevocable until the testator dies, and at that point it cannot be modified at all. A gift in the will may be impossible or fail, but the will is not amended or changed.