Subject says it -
Allow removal of a specific player injury, at least in Sandbox leagues, whereas now we can only cancel all injuries or none at all, allow us to delete in a case by case basis - I''m running my league in sandbox to test for various things such as statistical results, which is messed up if one of my key players is injured thus skewing the results

You can do that in sandbox by going to edit the player, and clicking remove injury.