Adopted use of the Funnies for US armies, keep everything else intact. If hindsight is permissible, retool the kind of firepower used on Omaha Beach so that it's effective as opposed to loud.
Have Ike tell Bradley that he's going to take the full range of Hobart's Funnies. Bradley is not allowed to argue about this and as a result the US casualties on Omaha are reduced by about 50%.
In addition have a staff officer who's been on holiday in the Bocage tell more people about it so that a counter to the hedgerows gets built before they set sail.