Moderation team found a solution, can we now start looking for the problem?
Encourage creative challenges, such as "engineers-only games" or "tech-3 only games" inspired by similar successful initiatives in other gaming communities.
What is the problem doing this with a regular account?
The player doesn't want to fiddle with its rating? Play an unrated map/mod (unit restrictions are sufficient). Or we just create an unrated mod.
Nobody wants to play with the player because the rating is too high? That remains the case, even if you hide the rating. But now the other participants just get a worse experience.
Only that one player is doing shenanigans but not telling the other players? I don't think you want to setup an officially approved "prank" game mode.
A better explanation why challenge account for challenges are required in the first place would be very helpful to understand the intentions.