Modernista! created Long Beach Brewing’s “This could be dangerous” positioning for last week’s launch of Thin Ice, a low-carbohydrate, low-calorie malt beverage. The Norwood, Mass., brewer, which created print, radio and in-store ads in-house, said it will work with Boston-based Modernista! on future marketing efforts for the brand. Thin Ice, which made its Boston-area debut last Monday, will roll out in several other markets, including Arizona, Colorado, Georgia and Wisconsin, before national distribution begins in April.