While the “legend rule” doesn't apply to permanents you control, you can control any number of legendary permanents with the same name and none of them will be put into the graveyard.
Mirror Box
The “legend rule” is the rule that states that if a player controls two or more legendary permanents with the same name, that player chooses one of them, and the rest are put into their owners' graveyards.
If you control more than one legendary permanent with the same name and the “legend rule” begins applying again (perhaps because Mirror Box leaves the battlefield), you'll immediately have to comply with the rule and put all but one of those permanents into the graveyard.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Néstor Ossandón Leal
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
