Isn't Delaware hunt horse country? If the area you are in is, you might be best to braid. If the open show is a regular one (held by a club, every year), you could check with the show secretary to see what the accepted version is. Or you could see if they'd give you contact info for "regulars" at the show and find out from them...
We've done pulled manes, no braiding (not showing breed shows at that time- wouldn't have worked to do both), pulled manes-single, small braids, long manes loose and long manes french braided. I learned the hard way to really thin the mane to allow the french braid to stay in, LOL. I LOVE the idea of the twists between the actual sections - I will have to try that out!
We used the halter I'd had made for this mare locally. If we do it again, we'd use her bridle and remove the reins - putting a double line/ring hook to the bit and a single lead (could even use the reins, just hook 1 end to the "y-split" at the bit). The riding class was after her halter and showmanship classes. We didn't remove the braid between since the classes were in the morning - almost back to back. We did keep her head up (no grazing) to keep her from pulling her mane apart. Yes, Magic is in foal. She had a beautiful Shetland filly in Jan 99. That filly went to a pony show series in Maryland/Delaware in 2000 and did well for us!
Here is a pic of our stallion when we competed in open shows with him. We have a large contingent of hunter folk here, so I did pull his mane that year to the proper length, but didn't braid him. He is wearing a custom made "stallion halter" that is fashioned after the ones Welsh pony stallions wear when shown. It was made by D. Lutke. He did well for us that year at local shows - and generated some nice pony sales for a time... I didn't have any purebred shetlands at the time (other than him and his daughter) - most were larger xbred ponies (1/2 shetland). I now know that even for open shows, I should have polished his hooves in at least a clear polish (I prefer clear since our ponies almost all have striped hooves and white socks - I don't like black hooves against white chrome, never have).
This is a daughter of the stallion above. She was always shown in-hand (halter and showmanship) with the bridle and reins - at several different open show venues. This was taken in 2001. We were told many times that the mane on the left is wrong - it's supposed to be on the right. However, I'd given up on "training" her mane - like her sire, right from birth her mane "insisted" on laying to the left. All of her full sisters' manes laid "properly" on the right side. Since we've sold her - the original purchaser put her with a H/J barn and they found the same thing - but they do the work required to "make" it stay on the right... This professional braid job is awesome!! I don't have a close up of her in hand after I'd sold her... W/ the H/J barn she is presented in a bridle when in-hand.
I thought I had a lot more pictures of our ponies braided with french braids, but apparently I don't. I even did a continental braid once on a 1/2 shetland/arab, took a while to do and I left it in all day simply because of the work entailed!! Pony stayed tied w/ a hay net and water bucket hung where could be reached. Hmmm....