No . You save your sims to library or cas and upload them as household from library or individual from CAS. If uploading them to the exchange , EA purges the exchange so even if you upload them, they may get purged at some point. Also if using CC , some CC is not transferable so what you may upload may not come attached with the download.
Technically they are "exported". Meaning that a "copy" of the sim (or rather the programming code which comprises the sim) is created & sent out of the game program. So the "original" sim (program code) stays in your game.
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