I'd destroy london with a big fuck off meteor. Then I'd fix human brains to realise that when people say junk food is bad for you, they aren't actually kidding.
Needless to say, industry, mass transit etc would all be obliterated and all the sites where factories, airports, railway stations or nuclear power plants currently stand would be replaced by cricket grounds, five a side pitches and ornamental gardens.
And I'd abolish DNA and replace it with some microscopic version of a USB flash key in every human cell.
And I'd give everyone six fingers per hand in case they were into slap bass or something like that.
And I would abolish Australia. Surely the real god must have put it there by accident, its rubbish.