(adsbygoogle = window.adsbygoogle || []).push({}); If im on 3.56 i cant like uhmmm download something or do something that will make me on 3.55?

No not at all your stuck there.

Well what you mean is called "downgrade". And no there is nothing like if you download something you will be brought back to the previous firmware.

There is a tutorial which shows how to downgrade your PS3 from 3.56 FW to 3.55, but the tutorial is risky, and you have to brick your PS3 to do it, so i wouldn't do it mate.

Once you update to 3.56, there is no going back... So, no you cannot.