In Things Fall Apart, is Okonkwo making up his own rules, regulations, and customs when it comes to Ikemefuna's death?

The Igbo cultural norms can be regarded as recommendations or as rules. Because every given situation will have some unique characteristics, Umofians do have some discretion about how they interpret those norms.
Three different aspects of culture come into conflict in the choice that Okonkwo makes to participate in killing Ikemefuna. The first is that his behavior to the boy had been as paternal generosity, so much so that Ikemefuma thought of him as his father. In addition, however, the gendered patterns of behavior are narrowly prescribed, and masculinity is associated with strength; Okonkwo fears that if the other men think he is weak, they will treat him differently in future. The third area has to do with the oracle’s power. Okonkwo fears not only the other men but the oracle: everyone should abide by its word, so he follows its pronouncement. In sum, Okonkwo’s behavior is consistent with his interpretation of Igbo cultural norms.