if you want a "perfect" immigration, do it before you meet sola/luna. cuz you dont want an event flag that mismatch the game version.
btw, use pkhex to edit the game version info and Time in the trainer tab.
So, I was able to convert my UM save to US, but for some reason, instead of having Altar/Lake of the Sunne, the Altar changed over, but the Lake is still from UM... Is there any way of converting the lake to what it should be, as in have it changed over from Lake of the Moone to Sunne? Hopefully that makes sense