Making BeerSmith describe Cereal Mash procedure is challenging. I simply create a recipe for the cereal mash which becomes an "extract decoction infusion" for the main recipe. It's simply a procedure description and log.
The cereal equipment profile is just a pot set at 100% efficiency, no trub loss. I set the cereal mash to Batch Sparge 0%, drain the mashtun. The gravity always shows 1.030.
In the mash I've provided, the protein rest is optional and only benefits the small amount of 6-row. It's perfectly fine to go straight to the upper end of conversion and skip the protein rest.
The main recipe should just show the malts minus anything you used to make the slurry. In turn, the slurry is only the grain weight used for it. The cereal slurry is shown with it's actual contribution of 1.020. This is due to it being half water bound with starches.
Within the main recipe, the slurry's ingredient profile is 1.020 because it's about half water. Your brewhouse efficiency will calculate this contribution correctly if your efficiency number is correct.
The mash has a decoction line, but it's named "Add Cereal Slurry." You'll just have to ignore the direction to remove any of the main mash. You should get about a 20 F degree rise in mash temperature.
Bonus points if you know who the recipe is a tribute to.