I'm looking to play Phantasy Star Online (and Ver.2) in future.
I'm Italian and my Dreamcast is a modded region-free US unit: plays anything (PAL and NTSC [US/JP] games) BUT without boot copies or changing swirl colour, like if any disc has the same region.. so I guess It's a modded BIOS(, right?).
Anyway, I discovered (twice) that PSO has some curious thing about Serial Numbers, between VMU files and this strange thing of the internal memory that saves anything like particular Connection options and other stuff.
I don't have the first copy of PSO used on mine DC, my console is used but in very well shape, and the original seller had PSO but only now (after two years) I discovered of this. So I guess I want to reset the internal memory of my DC for when I'll use a brand new PAL copy of PSO.
My existential crisis is... what EXACTLY I lose after I used the famous "DCFlash" other than the old Serial Number registered and the (old) Internet Connection settings? Can i risk to lose also my special region-free mod with this reset?

Also, before I use my brand-new PSO PAL copy, I must use DreamKey for the new Internet settings, right? Or can I do that when I want? I just don't want to play online now, but after a while I begin with the single player, also because I don't even have DreamPi too! (also, there are other alternatives if I want to play online?)
Also... my American Dreamcast is dated "December 1999", so that means.. can I play burned games too? If I don't remember bad, to play PSO's ONLINE mode I must use a burned copy... right? If yes, I must use a burned PAL copy? Or an US too?
Sorry for the english and long thread introduction, same for the many MANY questions. Hope to see answers for everything, and I hope that I don't forget any other things, if yes I'll make it!
I want to play this so much, and the things to take care for play PSO/Ver.2 now in 2021 are so many, or it's just me...
Anyway, thank you very much!