I had a similar idea some time ago, as I wanted to play "City of Lies" with my usual players group.
But for some reason, they were less than enthusiast with that idea (*), so I did not finish my work. It seems they had a very discouraging experience with a very "Japan integrist" L5R GM. Tea Ceremony seems to be a killer for those expecting 7 samurai or Ninja scroll...
MRQ2 has everything for running a Rokugani campaign :
-Cults for schools;
-Gritty combat system;
-Common magic for low-level techniques, spells and kihos;
-Legendary abilities for "high-level" school techniques and kihos;
-Either Sorcery or Spirit magic for magic and Maho.
You'll need to create 1 culture for each clan, using Land of Samurai ones as examples.
Bushi and Monk schools should give access to common magic at low ranks, and heroic abilities at high ranks.
Bushi "common magic" should be restricted to a short list, depending on the nature of school. You could also create two different skills for Kihos and techniques, the second being only usable for common magic learned from bushi schools.
Note that L5R magic is schizophrenic in nature. It is said you get magic by communicating with spirits, but you need to learn spells from scrolls to go beyond the effects of the 3 basic spells (which are close to). So, the best way to describe a L5R Shugenja is a Shaman that learns Sorcery. Of course, you could rename "Grimoire" into "Scroll".
As a consequence, Shugenja schools should give access to common magic (kihos, actually) and Spirit magic at low ranks, and Grimoires and sorcery spells at higher ranks.
Note that this is only a suggestion. You can also consider have a different take on Rokugan which is more in line with MRQ2, in which :
-Common magic and Kiho are the same, restricted to those with mystical knowledge;
-Three different kind of magic users exists : Shamans (Shugenja), Sorcerers (Mahô tsukai) and Priests (Kannushi).
