Not that I know of.

There are some hardcoded things in MTW (the golden horde/the swiss/the pope) which are difficult to change.

The only way of doing it is to change some region identifiers in the Script (move some east provinces to the west and visa-versa). This would fool the MTW engine and theGolden Horde would appear in whatever new western provinces you've assigned the eastern region id's to - the region id's that Golden Horde currently arrive at.

But, I DONT recommend doing this. It would be too make work getting the Script to work.