I'm assuming that code page 932 worked and you did find the text?
Do you know what I mean by find the text?
first what system is your computer using (I'm on 32bit vista basic)?
the system thing is important becuase it really is not that hard to get japanese support for your computer.
Get yourself EMeditor (it has multi-langauge support in it, it can auto detect the language from your dslazy dsbuff dumped files, from the rom you are opening (if it doesn't have compression, which is something else we will deal with later if we need too).
this is important becuase it will also tell you what table file you might need for your game, (utf 16le or whatever...), and from there you just google it and download that table file.
what I meant by find the text is that play the game and write down the text that you need to change or look for and use the hex editor to search for it...
the table file is useful if your to cheap to get an on screen japanese keyboard, you just copy and paste the characters that you are looking for in a new file in EMeditor, and then use this to search in the hexeditor.