"Were I not to live in Japan" implies to me something more subtle about how at some point in the past a choice or accident that landed you in Japan is the crucial factor in how much sushi you eat today, regardless of where you are now.
"If I didn't live in Japan" suggests to me that the reason you eat as much sushi as you do presently is the fact that you live in Japan now.
Of course, either idea can be written more precisely, and either option may have additional meanings or implications that do not necessarily require you live in Japan at the time you utter the sentence, but as a matter of suggestion these two do not mean the same to me, even though both are unabjectionable.
I do think you need "to," though. Otherwise, you may need "have lived."