Is there any rulebook that goes further in depth about Zellbringen and the honor codes? TW just does a basic rundown of it all.
Nothing that's currently considered "canon". Zell's gone through 5 or 6 rewrites, and the problem is always that the core of Zellbringen forces the Clan player to deliberately act in a non-optimal fashion, when the player doesn't really want to. It then has to figure out how to account for all the rules loopholes and edge cases that the motivated player is going to try and find in the Zell rules to get out of them...a task which is a functional impossibility.
The only way Zell works is when you have a rough guideline of what it's intended to be, a GM to adjucate it, and players who aren't going to try to work around the strictures, and who are comfortable asking the GM "can I do the thing?" Because here's the problem: not only does the above all make writing rules for Zell impossible...
but the way Zell works changes from novel to novel, author to author, and sometimes from chapter to chapter. It's not, and has never been, consistent, which, again makes writing rules for it literally impossible. And CGL eventually realized that, and basically gave up.
About the only new way that I can think of to make Zell function as intended in a non-GM'd game is to put portions of the novels into the Zell chapter as guidelines ("you should act about like this"), and give the opposing player full permission to kick the Clan player in the dick, twice, each time the Clan player is clearly gaming the rules.