I'm going to grill the chicken a day or two ahead of the event and want to park it in the boiled, cooled marinade so it doesn't dry out.
First, if you're using the marinade to serve the chicken, boil it down very well. Raw chicken juices are no one's friend! But I think I'd store the chicken separately from the marinade. (Well wrapped, it should be fine.) Depending on its ingredients - especially acidic ones - a marinade can break down meat fiber and effect its texture. You can use the boiled down marinade as a glaze to drizzle over the chicken when you serve it.
Good thoughts. Thanks very much.