Hi,
It is not possible to use importer 1.2.4 to migrate XF1.2 because there is only XF2.0 and XF2.1 in the drop-down menu.
We can only update from XF1.2 to XF2.1.4
So I have to change manually with an SQL command, it will take time but it doesn't matter, I'll only have to do it once.