[Emulgator]

Try it and see what your player does with it, YMMV.

First mux the BDMV folder structure, then add your files in <disc root>, write the disc.
Everything outside the BDMV folder structure should be ignored by the Blu-ray engine, so safe to add.

I did that with DVD many times for Extras like project files, Cover design etc.

The Blu-ray player engine should parse only for the known Blu-ray extensions,
so non-Blu-ray things even inside that folder structure should be invisible.

But I guess then these would not be visible for the media player engine as well.