There are quite a few of these, but I thought I'd try to create a list - feel free to correct errors
Had to start with the Flash family
Barry was first Barrence, then Bartholomew
Wally was first Walter, then Wallace
Iris' dad was first T.H., then Ira (I don't count William, as he's a very different character)
Wally's dad was first Bob, then Rudy (but I can't think when each name was established and if it was a pre-to-post COIE change, I'd count that as a different character like his dad, since he was very much reshaped)
Moving on
Alfred Beagle became Alfred Pennyworth
Hippolyte to Hippolyta
Steve Howard Trevor or Steve Rockwell Trevor
Mary Kent to Martha Kent