Yes, they do have more fireworks on the 4th of July. We spent most of the day at Epcot last 4th of July but headed to MGM for Sorcery in the Sky since it does not happen all that often.
From what I remember, on a previous 4th trip, they do the normal Illuminations show and then it is extended with more fireworks at the end.
Last year Illuminations was at 10pm since Epcot was open until 10pm but currently it is scheduled to close at 9pm this year on the 4th and Illuminations will be at 9pm as well.