For the most part, I don't believe that judges decorate their courtrooms...whichever unit of government that has jurisdiction over the facility makes those decisions, based in part on the law.One more time, courts of law cannot accommodate an possible endless series of ridiculous demands. If someone wants to change something the burden of proof is upon him. You don't see the damage in endless unreasonable demands and you could not even explain why your own ridiculous example was any different from the gold fringe idiocy. If you can't defend your own unreasonable example you only underscore why the fringe claim is beyond fringey.
For example, here in Illinnoying, the county boards are responsible for providing and outfitting the local courts. State law has some impact, especially concerning security and accessibility, but the county board uses its funds to buy whatever design they want to have, and decorate it as they decide. The judges are locally-elected employees of the state. They are welcome of course to make suggestions about decor, but unless it's specifically mandated or prohibited by law, it's not up to the judge.
A "sovereign" would maybe have more luck trying to convince the board to use flags without fringe...but I'm doubtful.