Dynamic Code of Honor?

[Haserway]

So, I want to create a character with a certain frame. The best example woule be, I guess, the Ghost of Tsushima. The character has a Code of Honor (samurai), but struggling with harsh reality of war and has to seek a compromise with himself all the time, utilizing dirty guerilla tricks and tactics (stealth attacks etc), which confronts his Code of Honor.

I want to make a mechanic that would represent his "downfall", when he comes to "dirty" tactics and his "enlightment" when he goes along his Code of Honor and fights fairly and openly.

Firstly I thought about Higher Purpose. That would totally ignore his Code of Honor, though. So I'm a bit in confuse now.

Could it be also, for example, a system that has dynamic value of CoD? Closes example is "Humanity" in VtM. If so, how could I make it work in GURPS?

Any advice is vital and highly appreciated. Thank you!