If you can't remember what edits you did to get yourself shadowbanned, you're better off with a fresh save. Keep copies of that fresh save if you screw something up and end up shadowbanning yourself. Restoring one of those saves will remove your shadowban.
As someone said earlier, it requires either ROM/hex editing, but the moment the online servers realizes that you have Shiro w/Raijinto and Siegbert w/Siegfried, it'll shadowban you. It's not in the game's code to have the royal children be able to wield their fathers' weapons. That's a DLC only trait. Even the weapon descriptions say "Ryoma only" or "Xander only."