Who follows the letter of the law and who follows the spirit of the law in chapter five of To Kill a Mockingbird?

There is no overt legal implication concerning the events in chapter 5. The only thing somewhat related to a legal issue is, perhaps, the right to privacy. When Jem, Dill, and Scout try to get a note to Arthur Radley, they are hardly being a nuisance, but I suppose one could argue that they are invading the Radleys' privacy.
Atticus recognizes the possibility that Arthur and/or Arthur's father might interpret the children's games as harassment or some kind of invasion of privacy. Given that these are kids playing fairly innocuous games with a recluse, I wouldn't think that the "letter of the law" really applies here. However, for argument's sake, if anyone is following the letter of the law and the spirit of the law (in chapter 5), it is Atticus. It seems pretty clear that Atticus is just trying to save Arthur any further ridicule. (At this point, Atticus has no idea that Arthur finds some of the children's antics amusing: Arthur is heard laughing at the end of chapter 4.)
The letter and spirit of the law become very significant in later chapters. Does the jury follow the letter of the law with regard to their verdict? Do they follow the spirit of the law, for that matter? In the novel, who breaks the law and gets away with it, and why? There are plenty of interesting events that concern the law later in the novel.

Atticus follows the letter of the law throughout the book. Only at the very end, when Bob Ewell is killed, Atticus insists that the law must be followed. It is the sheriff Heck Tate who convinces him that in this case the spirit of the law is more important than the letter. Scout understands and tells him essentially that forcing Boo Radley into the open after he saved their lives would be like shooting a mockingbird.

Miss Maudie is a character who rarely follows the letter of the law but follows rather the spirit. This is particularly true of her in regards to the rules of her religion. She is Baptist, and when others complain that she doesn’t go to church enough and spends too much time gardening, she basically responds that she is in God’s outdoors, implying that she is following the spirit of her religion, not following the Bible literally.