The usual method is not "building it up" and feathering is pretty much impossible- it's drop-filling the gap (after dye is used) using thin viscosity CA and a pipette with a fraction of a mm spout. Once the gap is filled *then* the high part is gently scraped with a cabinet-scraper shaped razor blade. Most of the blade is masked with scotch tape; only about 2mm or so of the prepared blade is exposed. The tape prevents damage to the surrounding coating. Once the area is as level as possible - and sometimes it takes two or more passes of drop-filling/scraping - the area is polished (wet sanded starting with 2000 or finer if necessary, but a clean scraping job doesn't usually require any sanding). Scraping with an unprepared and/or unmasked razor blade almost always results in unwanted scratches and/or damage.