First things first - no error when exporting.
Here are the results:
Both are very similar, both throw no error in ksp.log but now none of the 16 portraitCameras can be found:
The original mu has 2,148,245 bytes. After import/export both end up a bit larger: 2,454,640 bytes. I wasn't expecting the same size but with rearranging the data and no deeper knowledge about the format I would have to start from scratch analysing the files. I hope you can fiddle it out. Or in case you create different, hopefully correct results you can tell me how to avoid making something wrong.
Sorry for not mentioning before, it's a clean KSP install, no mods.