I'm choosing a Level II program tomorrow and just have a small question. If I'm interested in doing a double major, is there any way of inputting this on Mosaic, when choosing my program?

If it's one of those preapproved double majors in the undergrad calendar, it should show up. Your selections are done in the form of drop-down menus, so there's no way to indicate anything. By the way, it says that program selection begins on the 30th, not tomorrow. If none of the options that show up apply to you, go see your academic advisor since it doesn't close until april 30th (or even anyone who works in that office).