I agree with everything posted so far, but I would like to add land/agricultural reform. While not as important as some other issues, this was a real problem in pre-war Japan. A lot of the support for ultranationalism came from rural youths, many of whom turned to radicalism as a reaction to the extreme poverty of the farming communities, even during the "good times". The small-scale farmers could never compete with the huge estates. Historically, some attempts at land reform were tried, but always failed because of the political power of the wealthy. When the Great Depression came along, rural incomes fell even further, and support for more radicaal solutions to Japan's problems grew.
If some small measures could to taken to convince the rural masses that, at least, their children's lives would be better, you would create another class of people content to support the Taisho Democracy status quo. Without radicalized rural youths swelling the ranks (esp. as low-ranking officers) of the IJA, the military likely remains just one power bloc among many. Japan may still be tempted to expand when/if the other great powers are distracted by war, but it should remain a reasonable, predictable power.