My recollection is that the Illuminations tag runs only Independence Day, but at least in recent years the MK fireworks run at least one or two other days in addition to Independence Day. If that trend continues, you should be able to see both by going to Epcot on July 4, and MK on one of the other days.
My advice would be to keep an eye the Disney Parks Blog. I think they announced the schedule of events there last year - although I don't remember it being very long before the event - maybe a week or two. Actually you can probably find out by browsing the blog archives.
Here's a link to one of several parks blog posts from last year. It's not the actual announcement, but it references and I think links to it. Start here for a look at what they did last year, note the dates of the posts, and start watching the blog around the same time this year.