Don't do it! Relics like that are much more prized in their original (read worn) condition.
For this exact reason, I hope you decide not to.I feel like I would wipe away history...in one stroke if I did....
If you want shiny ones you can get new ones from his branch of service. When my Grandfather passed we went to Ft Leonardwood to get his WWII records for his Military Funeral and discovered he had several medals that he never told anyone about. We were able to get the 3 sets of medals for his 3 children to place in a shadow box for each. Needless to say everyone was completely suprised of the amount of medals he earned during his service and had never told anyone.
That's just the way he was.......humble.