Adding page number info to KFX without converting

I'm interesting in adding Kindle page numbering info to KFX files. What I'm hoping to avoid is having to use the KFX input/output plugins to convert KFX-to-KFX in order to use the feature that adds this. While I'm sure this works fine most of the time, I'd like to leave the books exactly as they are without risking introducing formatting issues.

Is there any information about exactly how the KFX file format stores this? Is looking through the corresponding code in the KFX output plugin my best bet?

Thanks for any advice or pointers.