>How would someone go about making guns an acceptable solution to problems in the eyes of Rokugan society?
Easy. If the Emperor likes something, everyone likes something.
In my L5R campaign setting, I use 7th Sea\Theah for my Gaijin. After White Stag (which was actually a religious crusade instead of greedy infighting), the Mantis retained sole (secret) trade with Theah, and became stupidly rich in the process. However, around the 1120's, someone found out that the mantis were doing this. A fast thinking Gaijin trader, a Vodacce, along with his Fate Witch wife, moved first, asked an audience with the Emperor, and because of his wife's powers, not only was he seen, but the audience went spectacularly well. Old Hantei Jodan, so bored and beaten down by all the childish clan squabbles, found his inner child again after becoming so enamored with the Gaijin.
So, Gaijin trade opened up, with some pretty heavy rules, notably no Gaijin can be harmed on Rokuagni lands, but the Gaijin are hard forbidden from spreading their Vaticine Religion.
Firearms are now finding their way into Samurai armies, and only a couple clans, most notably the Lion,refuse to have anything to do with the Gaijin at all.
The Mantis got completely cut out of the loop, since the Vendel League no longer has to get fleeced on prices - so now that the Mantis standard of living is crashing, their basically turning over to full piracy against the Gaijin trade fleets - this of course is making the Mantis one of the most technologically advanced militarys in Rokugan, since they can loophole attacking the Gaijin, and they've begun outfitting their ships with stolen cannons and muskets.
But really, Gaijin work a lot better when you use 7th Sea, considering those nations have heroes as well as villains. Merenae and Thrane just always reek of being complete villian assholes