If you are really worried go ahead and change it back. The worst thing that will happen is they would start IP banning MAC addresses that will permanently ban your whole console from going online. They WILL NOT brick or fine you for CFW, trust me they would have a lot of lawsuits if they did.
I really doubt they will even start IP banning consoles to be honest.
They can't fine you for running custom firmware. You could possibly be banned however. If you have been running a custom firmware to run modded lobbies I dont think its a ban. Running backup manager and running homebrew might get you a ban stick though. I really wouldnt be too worried about it. Just change it back to regular firmware if its your only PS3 and you should be fine.
Nothing You might get blocked from PSN until you download OFW 3.whatever. If they did brick your console they would have lots of lawsuits. And they wouldn't want that because they are currently at court with Geohot and Fail0verflow