She waited 20 years to make the alterations. So i guess she was quite pleased with the original state during that period of time.
Sophie was later showered, literally, with jewels from HM's personnal collection. So to insinuate that the wedding tiara was some kind of a snub is just pure nonsense.
But she rarely wore that tiara during the 20 years.
Maybe my memory is faulty, but I only recall her wearing the wedding tiara more often after it was changed.