If your concern is that seating will scrape the coating off the boolits, no worries! All that I have coated have withstood the seating process with no damage to the coating. All mine are coated with either harbor freight red, or powder-by-the-pound harley orange of wet black. The coating is a very tough layer, it even survives the cutting action of the rifling. And expansion of a hollow point.
There's several ways to flair the mouth of rifle brass. Both RCBS and Lyman make case neck expander for rifle. Lyman used to sell either a long or short "M" die body that you could then buy the proper caliber expander button for your rifle boolits. NOW they sell a caliber specific die, more money in their pockets. RCBS goes the way Lyman used to go, they have one die body, then sell the caliber specific expander buttons separate. And then along comes lee. Their expander die is simply several tapered bellers, similar in what a handgun belling die does. It's universal, can be configured a bunch of different ways to bell just about any rifle case.
Another trick I came up with once was to use a pointed FMJ bullet one caliber bigger than what I was loading, IIRC it was a mauser .323, used to expand/bell a 30-06 mouth. I set up the seating die, put the FMJ in the case mouth point down, IE backwards, then just seated it enough to form a bit of flare in the '06 case mouth. The bullet was easy to remove. A lot of work, but when you don't have the right tool, improvise!