simple question

[s3rgio]

Can I play on xbox live with originals after flashing my lite-on?

[neonpolaris]

Can you search before you ask?  This question has only been answered 1000 times here.  It would have taken you less time to find it by searching than it did for you to register and ask.

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That being said, let me break it down for you:
There are no 100% guarantees about not being banned.

Now let me answer all of your next questions..

It doesn't matter if you disconnect from live while playing backups.
It doesn't matter if you pull your network cable while playing backups.
It doesn't matter if you double-check your "stealth" with mulleter and/or abgx.
It doesn't matter if you never even play a backup game at all.

If you have a flashed firmware, there is always SOME CHANCE you will get banned.

Simple steps to lessen your chances of being banned:
Rip your own games only.  Downloading is a crap-shoot. (and not to be discussed here) You don't know for sure your playing a review copy.
Use a Kreon drive, not the swap method.  Again, downloading any part of the image is a crapshoot.
NEVER play a game before it's release date.  Ever.  Again, I don't care if you disconnect from Live.  Don't do it.  If you only rip your own games, this shouldn't be an issue.