Moses wrote Gen. 9. The was an ancient near East during his time and the “blood avenger” question was a prominent feature of the Hebrew people.
The case concerning the woman caught n adultery is a death penalty case. It is the incident where Jesus changed the OT law concerning the implementation of the death penalty. No longer do the two or three witnesses implement the death penalty, it is the one without sin.
Saul/Paul conducted his persecution to the death of Christians under the authority of the Sanhedrin: the ruling body of the Jews. It was murder, nevertheless, unless you believe the killing of Christians is not murder if a government sanctions it.
Moses was a prince of Egypt, but if you hold the Gen. 9 passage presents an absolute establishment of the death penalty for murder, Moses is not exempt because he was a prince of Egypt.
peace to you
Moses merely wrote the history handed down to him. There was no ancient near east in Noah's day. The commandment came from God, not Moses. Furthermore, Moses is not even the author of the Mosaic Law but God is. You are echoing higher criticism.
Genesis 9:6 deals with the death penalty for murder only. Period. Adultery is not murder.
As you imply, Saul had legal authority. He also operated under Roman auspices so your example does not make sense.
You also downplay the status of Moses as an Egyptian prince and general. It is as if you were saying that Nimrod did not have tyrannical powers. Moses could not have been convicted. He fled to Midian because he renounced Egypt. His renunciation affected his legal status but upon his return to Egypt he faced no criminal charges for murder so your conclusions are again amiss. There is no legal change from Noah to Egypt. And there is no legal change from Mt. Sinai and Jesus clarified that he came to fulfill the law and not overthrow it.