Coating fibro products is not recommended. You should only coat fibro products if they're in sound condition and then only to waterproof them.
risks associated with installed, undisturbed asbestos products are small. Even weathered asbestos roofing does not release much airborne fibres unless the material is either disturbed or handled in a way that promotes the release of fibres.
coating is not considered necessary on health grounds. Surface coatings, however, can extend the life of asbestos products and may improve their appearance. Special sealants only should be used on asbestos material as ordinary paints do not bond well to the surface of weathered asbestos cement products. Use a professional painter, where possible.
to check if your asbestos roofing (like all roofing) needs to be replaced. Roofing that has weathered to the point where it is structurally unsound and no longer waterproof should be replaced. Use a registered asbestos removal contractor particularly when the area is greater than 200 square metres.
if you decide to coat your roof, put planks down so that people do not have to walk directly on the roof.
wear full protective masks and overalls when working.