Personally, when I Cerakote (or paint is the same) areas like that on lights/optics - I give zero f's about that tiny amount of Black, and I cut a circle of Pelican Foam to keep the lens clean.
Or you can get meticulous with Painter's Tape and an Exacto Blade.
Never tried, but thought about: Carefully coat the Lens with Vaseline?
Probably a good post for the Refinishing Forum.