Self-fulfilling stereotypes: Have researchers tried inventing new group stereotypes? Studies on the stereotype threat have typically used stereotypes that that are common in contemporary culture, i.e. the canonical example being the study that showed African American SAT scores lowered when faced with the stereotype that African Americans are less intelligent than other groups.

Have there been any studies where researchers invented a stereotype (i.e. something random, like "Hispanics perform more poorly at jump rope than other groups") and tested to see if it had any effect on well controlled test subjects?

Have there been any social studies where scientists have tried inventing a new stereotype and implanting it into the mainstream population?  (I doubt this because of ethics issues, but it would certainly be interesting!)
The "blue eyes brown eyes exercise" involves a completely arbitrary and invented stereotype.

During part of the exercise, Jane Elliott treated the blue-eyed children as the superior group.
The following day, Elliott reversed the exercise, treating the brown-eyed children as the superior group.
She treated people with the superior-eye-color-of-the-day as highly intelligent and able to learn,
and people with the "inferior" eye color as inherently lazy and stupid.

I hear that, during the exercise, the new stereotype does have a significant effect on the subjects.

Perhaps this exercise by a schoolteacher doesn't really qualify as a "well controlled experiment" performed by a "scientist", but it sounds pretty close to what you were looking for.