/bgui reload (or /bguiproxy reload for Proxy setups):
Reloads all menus and their configurations without requiring a server restart.
/bgui open [menu_name] [menu_params] (or /bguiproxy open [menu_name][menu_params]):
Opens a specific menu for the player executing the command, with optional params if needed.
Permissions
bedrockgui.admin:
Grants access to admin commands, including reload and open.