A typical example used by a canny few is to warm-up for the dressage in a pelham, and then swap to a permitted snaffle at the last moment.
It’s not ideal, you’d prefer to get the horse properly through and working correctly in the snaffle, but as we know, some horses can be very tricky! I have seen a horse at Burghley being worked in a pelham and dressage saddle, so even the great do it when necessary.
Obviously you must make sure to swap to permitted tack for the dressage, before your test!
Photo by Steve Bell.