first you announce that they will
why western personal law? lolzzzzzzzzzzzzzzzzzzzzz if you are opting to adopt an alien law then whats wrong with having that of Muslims, Sikhs, Christians, which they are already practicing individually at community level
oh really and how will you do that ?
Till recently Sikhs were forced to register their marriage under Hindu law which was not acceptable to them so you had to atlast approve theirs.
Now how will you impose uniformed civil code viz a viz personal alws?