I wouldn't consider a hard and fast arrangement for every time of singing. Although occasionally I will stick to a particular decoration or tune variation for a particular verse each time of singing as it heightens the words in some way, or just feels right, generally variations of tune/decorations etc will be spur of the moment "what feels right now in the moment" things. (Sometimes also dictated by state of the voice - if getting over a cold and having lost the bottom register to some degree different tactics may be required!!!)