Unfortunately damage like this is irreversible. It may cause structural issues over time. Trees with thin bark such as maples can split during the winter from rapid freezing and thawing from direct sunlight. The best thing to do is allow the tree to grow around the damage and do what you can to protect it from future damage and stress. I would suggest contacting an arborist since this is a memorial tree. There appear to be some problematic crossing branches that could be an issue in the future. An arborist can help you come up with a long term plant for preserving the tree. 

An arborist can be found at the following site.
treesaregood.org