If I were Eru and wanted to have some fun with the Middle-earthlings.... and btw I have a twisted sense of humor...
-I'd bring Morgoth out of the Void and make him invincible
-I'd transform the orcs into men with superhuman fighting abilities
-I'd give Angband and Mordor modern weapons
-I'd make Denethor fireproof
-Just for kicks, I'd drop an open bottle of Clear Eyes onto the eye of sauron
-I'd call the fire department and have them put out the eye of sauron....
-I'd put Valinor back within reach of the world and make the defenses obsolete
-I'd give Sauron the Ring
-Or, I'd give MORGOTH the Ring
-thats all for now, dont wanna overdo it