Registering a new EP on the Official Sims 3 Page

[jeanamariex3]

Do I have to do it before Playing that Expansion pack? I currently am trying to register LN, but the Sims 3 Official Website is down. Will I still be able to play before I register my game? Or do I have to wait?

I also paid for this game off the EA/Origin Website, and it's currently installing, so just so were clear, this isn't a pirated copy, this is a digital legal copy.

[Ausette]

I think you can still play, but the website won't recognise the fact that you have the game, so your uploads and downloads may be affected. You also won't be able to claim the registration rewards. I'd recommend registering as soon as you're able, the website's back up for me now.

[PJSim]

... so your uploads and downloads may be affected.

No, that will work fine. I played for a long time with only the base game registered at the site.
And when I first bought the game I played for quite awhile without being registered at all, you don't need to upload or download anything to just play the game.

All you need is to register one of your games at the EA site in order to get an account, I assume you've already done that. After that registering the rest of your games doesn't really do much except give you registration rewards, if any, it's not necessary at all.
All it's really good for is if you should lose your serial number at some point. Then EA will be able to see that you do own the game and should give you a new code.