Based on the original design, this will require some work to both retain the current function and not require script changes for the original mods, but also add some flexibility to achieve what you want.
The shading effects are hardcoded for the guns/blades. They are also hardcoded for the character. As you found, you can override the effect name for a model if you obtain the whole model object in the scripts and send that message, but of course it only provides the entire character model. So you cannot add the lenses as a part of the character model; it will need to remain separate, so that you can pass an effect name for just that piece. But how to "attach" them in the correct position of the character model?
We did add a way to add a hat, or piece of headgear to a character, and a way to adjust the position relative to an existing "locator" defined on the character. All the characters have a "camera" locator for the eye position, so we added a way to adjust the hat position, relative to the camera locator, by reading an x, y, z adjustment. Since this adjustment might be slightly different for each character model, we had to devise a way to read the character model, read the x,y,z adjustments for that specific model, then move the hat to its desired location. Means we have to manually check each character (which we have not yet done...only some of them), but it's a start...
Anyway, there is also already a way to "tie" random items to a specific locator to a character as well, which is why the characters in taverns can hold food/drink. Those items also adhere to the 2 hardcoded effect options in the engine (they are EnvAmmoShader and AnimationBlend if you're curious, and they are chosen whether the highest bits are part of the alpha value supplied by a "render tuner" in the engine). What I'm thinking is that we can add another "tie" feature that is similar, but "extended" in that you can also adjust the position like we provided for hats, but also provide a specific effect name if you want also. This way you could also specify the "camera" locator for your lenses, but every character model would need that x,y,z reposition in a file (see ERAS RESOURCE\INI\pscriptsRESOURCE\INI\pscripts\HeadGear.ini file for the hat example), then also specify the effect name you want to use for that item.
I have no timeline I can give you for this, because I am fulltime employed at a job and can only devote part time to this, but I'll add it to a list of features to add.