From my testing it is possible with rogero and rebug 3.55 downgrader .999 .PUP, I've done it and worked but when you do it is not easy to upgrade from that. I tried everything and took awhile to finally work, it gives you and error when trying to upgrade From xmb update and even safe mode. I was able to get it up to 4.41 cfw but wasn't able to go higher back to 4.46 cfw. I used other ways but ended up causing s fake GLOD an even RLOD as well both being fake cause of software corruption.
I've tried other ways to fix it from it also was turning off by itself and I fixed that to now it turns off lol. Well I got that fixed to but now I get solid Green light and after Sheila will start blinking, mind you from the start there isn't any video hdmi working and it's not going into XMB start screen as well. I'm now stuck and tried also with another ps3 to let it reformat it and worked on that one but doesn't work on the other.
I believe I have just made a software brick crash that causing the problem, I'm going have to wait for something new to fix this or have someone with more knowledge take a crack at it. For now I don't advise anyone downgrading besides pretty much all newer stuff working without patches is nice. I hope I helped someone from not doing what I've done when testing the software out.