So, there is the mod Need To Breath, which makes the world toxic. However, I was thinking that, In alignment with This suggestion, there could be a filter for the mouth, to decrease the toxins, and the effect!

However, it's ultimately your mod, and your decision.

That's actually something I'd wanted to add support to in rewired, as well as deep resonance. Unfortunately, the way that those mods handle checking for either a respirator or anti radiation armor can't work with augments

Well...

With some work, maybe you could.

Here is an idea that might work (I haven't gotten into moding yet, just haven't had the time)
So, maybe you have a "hidden" armor slot. That slot can't be accessed, but basically, when the module is active, it puts in a piece of armor that gives the effect. It looks like the module is doing it, but you are just making a new radiation suit, similar to the one in that mod, and then making it controlled by the module. I don't know if that would work, but maybe it would be a starting point?

An hidden slot to the player would still be hidden from the other mod.
From the look of it, this is bug in that other mod API, ask them to fix it.