Hacking ROM Hack Wii Fit Plus text editing

[UltraHylia]

Hello,

I'm trying to edit the text in Wii Fit Plus.

I've found the health_message.bmg file inside message.carc, but I'm struggling to edit the file.

PikminBMGTool says it recognises the file, that it uses latin1 encoding, and doesn't show any errors, but the export it produces doesn't contain any of the game's text. I've tried CTools BMG Editor and wbmgt (Wiims BMG Tool) and am having invalid data errors with both.

CTools BMG Editor:
"Load editor
Found invalid data while decoding"

wbmgt:
wbmgt decode health_message.bmg
!! wbmgt: ERROR #36 [INVALID DATA]
!! No BMG file: health_message.bmg

I'm running wbmgt in the same location as the bmg, and I know it can see the file because it produces a different error message (#72. 'No such file or directory') if I input a file name that doesn't exist.

I'm guessing the encoding of the file is a bit atypical but I'm struggling to figure it out. I can load the file into a hex editor and edit the text that way, but I'm going to be making very extensive changes to it, so that isn't a realistic option for me.

Thanks!