Magnesium is extremly corrosive, you really need to give this to a pro.
Dymag used to do this on all wheels until a t0sser complained, got his wheel redone, complained again, got his money back and then went to sell those on ebay proudly saying that they had been refurbished by Dymag.
Now Dymag will not refurbish anything that isn't Dymag (understandly so).
Dymag recommended me
http://www.realitymotorworks.com/ They are in Bristol (ask for Nick). They have done a mint job on my mag arm / yokes and wheels and are very reasonably priced. Cool bloke as well.
That said, if paint has bubbled up already it is likely that the end result will not be totally mint. You will still see marks where it originally bubbled. Don't expect miracles.
p