We always found that our butlers appreciated the requests made in advance [much easier than changing a set up later] and kept a copy with them.
Frankly, requests are [or should be] personal to the individuals. For example, we like the bed in the PH [which do not split on S-class ships] to be made up with individual [single] bedding. It stops us fighting over the quilt and works for us but is not what most people would want. Other requests we have made would also not suit others.
My advice, therefore, has always been to think of what would make your cruise great rather than what butlers have done for others. If it is within their power to do it, they will but some things are not possible. If an item is not on board and they cannot source it, they cannot provide it. On one TA the plastic carrier bags [US = shopping bag?] had not been delivered to the ship before we set off across the Atlantic. No amount of goodwill could produce a bag on that cruise.