Hey i'm working on a ranked system for my game, how can I hide a hud message device for one player only?

In that case you have an easy solution. Hud Message Devices have a priority system (lower is better). You can give your hud message device with the Bronze rank a priority of 10, your message device of silver a priority of 9, gold 8, etc. This will only show the Message device with the lowest priority. Make sure the setting ‘layer’ is the same value for all message devices.