When rituals are changed, we can understand that in the view of those practicing them, the parts that can be changed are not essential to the effectiveness of the ritual.
The parts that cannot be changed are the permanent core of the ritual. Of course this depends on the people involved.
In the case of a wedding, for example, while some people may wish to have a new style wedding, they may still include an ritual authority who directs the activity (like a priest), and the bride and groom may each have assistants (best man, and bridesmaids, as in a traditional wedding.