Brew it as written is my advice, see if it works. You have already changed the OG. The last 2 malts will mainly add color.
The crystal malt rule is one I often follow. I broke that recently when I brewed a tmavý ležák, 10P Czech dark lager, following what I could find online. It used 15% caraBohemian, and has good body for a 4% lager. The 4 pro Brewers that had it at a party though it was really good. You can try it at club night if you are going to HomebrewCon, as my club decided to do all session beers.