FWIW...

I made this up and then while researching traditional Scottish wedding ceremonies came across almost the exact same ritual for my daughter's upcoming wedding:

The bride-to-be and my wife will wear tartan rosettes in MacQueen. Both will have broochs to hold the rosette--the bride's will be a thistle/clan badge and my wife will have an antique sterling penannular.

The groom's mother will wear a rosette in red MacFadyen with, presumably, a clan badge brooch. The groom will carry an extra MacFadyen rosette. At some point in the ceremony, after the vows are said, the groom or the groom's mother will remove the bride's rosette and replace it with the MacFadyen rosette, using the MacQueen clan badge brooch--thus symbolizing the simultaneous merging of the families and the bride "cleaving to here husband" and becoming a MacFadyen.