Announcing changes on the FMA and thrust mode display when they occur is a good CRM practice." from b777 OM.
Every word of advice in Boeing manuals is closely scrutinised by the company lawyers to ensure if someone bends the aeroplane, the finger can be pointed away from Boeing. Announcing FMA changes is an example. A few years ago, the manual would use the word "verify" which means use your eyes. But lawyers could pick holes in that and now they advocate "announce" so it goes loud and clear on the CVR. It has nothing to do with so called good CRM practice