(a) Unless the terms of a trust expressly provide that the trust is irrevocable, the grantor may revoke or amend the trust. This subsection does not apply to a trust created under an instrument executed before the effective date of this chapter.
(b) Unless the terms of a trust provide otherwise, if a revocable trust is created or funded by more than one grantor:
(1) To the extent the trust consists of community property, the trust may be revoked by either spouse acting alone but may be amended only by joint action of both spouses;