By Francesco Guarascio and Robin Emmott BRUSSELS (Reuters) – The European Commission proposed changes to its planned embargo on Russian oil to give Hungary, Slovakia and the Czech Republic more time to shift their energy supplies, EU sources said, although failed to reach a breakthrough on Friday. The EU executive set out the embargo this week as part of its toughest-yet package of sanctions against Russia over the conflict in Ukraine. But Hungary and other EU member states said they were worried about the impact on their own economies. The tweaked proposal – which EU envoys discussed on Frida…