The photos of Queen Mary on her wedding day do not really support that theory Franck.
Based on the photos I think that Queen Mary was wearing 3 separate bracelets on her left wrist, one of which has a large cabochon stone surrounded by diamonds. One of the bracelets appears to have been plain (perhaps a gemstone feature was hidden) and the other, third bracelet appears to have a pearl an diamond motif in the centre.
Detail from the above photo
Detail from the photo immediately above.
Queen Mary was photographed wearing the same bracelet with the dark cabochon stone surrounded by diamonds in photos taken just before her wedding and in the years after.
There was some comment in press articles that King George had given her an emerald and diamond bracelet on a curb link gold bracelet as an engagement gift instead of an engagement ring, but, so far, I have not been able to find any definitive proof. I wonder if it could have been this bracelet.
Photo said to be taken in early July 1893.
Detail from the photo above
Detail from the photo above
As Duchess of York
Detail from photo above
What ever bracelet Queen Mary wore to her wedding and in the other photos, it definitely does not match the bracelet given by the Tsar and Empress.
Bracelet given by the Tsar and Empress
In the photos of Queen Mary wearing the other bracelet it can be seen that the shape of the cabochon stone and the diamond border is different from what can be seen in the brooch (from modern photos) and that the section of the brooch with the large diamond is missing in all cases. Yet, there is nothing to suggest that the central element of the bracelet, now worn as a brooch, has been changed in any way.