You don't have to do allergy testing to see if she is allergic to corn. Ellie has never had it... Her vet looked at the ingredients in the Royal Canin and said she thought is was the corn.
She has told me that allergy testing is a long road that I probably wouldn't want to get into. And she's right.
If your dog itches on a food, pull it. If it is a complex kibble and you don't know what ingredient she is allergic to then pull all of it for a few months and reintroduce individual ingredients to see which one she reacts to. If you are sure it is the corn, then it is the corn and there is no reason to do this.
I elected not to use Actigall with Ellie. One of the reasons is it does alter bile acid numbers and I want to get good readings. I might go with it someday though. Retesting bile acids will be pretty close to pointless (but maybe still necessary) for Samie now.