Rules:

• History of the world before your birth remains the same; only events happing after your birth can be changed.
• The other version of you must still be alive, you cannot go to a world that you are dead in. (This essentially forces you to murder/abduct your alt-self, so travelling has a ethical cost to it 😉)
• There may be other multiverse travellers out there

(Btw, is it ethical to murder an alternate version of your self? Is that even murder or just self-harm technically?)