I doubt anything could "happen" to you as a result of this letter. I learned of the UN affiliation through an elder's wife who, in her total and never-ending blindness, justified the WTS and their need for a library card! This was before I started to fade, but had already had plenty of doubts and was just exhausted from all the cognitive dissonance, so what she told me ended up being the second-to-last nail in the coffin as for my allegiance to the WTS (the last nail was the pedophile/SilentLambs information I gleaned from the internet).
Therefore, if the rank and file are aware of the UN affiliation (my "friend" got her info from ones she knows at Brooklyn Bethel), then what you wrote is in no way "apostate".
I hope your mom isn't as blind as my "friend".