Question [Q] Possible recovery of Jelly bean through motherboard replacement?

Hello all this is just a query on forcing a reset of the phone though going to a centre and asking to have the motherboard switched, currently I managed to get a sm-n9005 via gmarket in Korea, it arrived and it turned out was actually a UK version of the phone, (which conveniently is also where I am originally from).

So to cut it short since Im not the first or the last who has got this now neutered phone, I stupidly updated to Kitkat before reading up on it here (I figured I could trust the companies) and lost 8 months of work that was stored on Action memos.
I cant get it back and also found out I cant get back to Jelly Bean.
Now I understand that there is discussions on working out how to either fix knox or crack Kitkat to get the option to downgrade under way, and I look forward to all that when its eventually worked out.
However it occurred to me that what if I just walked into a service centre and asked to have my motherboard replaced?
Wouldn't that mean I would get a reset back to JellyBean and back to 0x0 on Knox?
I'm not tech savvy enough to know this for sure and there is varying opinions on what kind of service you get at various stores, but if I were to get it replaced, that would fix the problem wouldn't it? Its not a cheap or normally practical solution,but now I cannot use VPNs or have reliable gps or even store my lesson work on my 64gb sd card (unless I root it again) the phones basically become a very expensive toy/phone.

Also which os would be a nice alternative to any of the stock versions (im thinking of giving Ubuntu a try), something that removes the bloat ware but keeps things like the s-pen wheel functions and multiwindow?

Thank you for your time in reading this.