The Question and Answer section for Sir Gawain and the Green Knight is a great resource to ask questions, find answers, and discuss the novel.
The Green Knight extends his challenge to anyone who will take it. In the challenge, any of Arthur's knights, or even Arthur himself, will strike a blow against the Green Knight, on the condition that they allow him to strike back one year and a...
Gawain expects the sash (girdle) to protect him. The Lady told him that whoever possessed the girdle couldn't be killed.
You certainly can choose the codes of chivalry and to what extent Gawain adheres them. Gawain does a pretty good job. You might pick three codes of chivalry like honesty, purity, and never refusing an honorable challenge.